Highway Noise a Design Guide for Highway Engineers

NATIONAL COOPERATIVE HIGHWAY RESEARCH PRO6RAM REPORT 117 HIGHWAY NOISE A DESIGN GUIDE FOR HIGHWAY ENGINEERS

HIGHWAY RESEARCH BOARD NATIONAL RESEARCH COUNCIL NATIONAL ACADEMY OF SCIENCES -NATIONAL ACADEMY OF ENGINEERING HIGHWAY RESEARCH BOARD 1971 Officers CHARLES E. SHUMATE, Chairman ALAN M. VOORHEES, First Vice Chairman WILLIAM L. GARRISON, Second Vice Chairman W. N. CAREY, JR., Executive Director

Executive Committee F. C. TURNER, Federal Highway Administrator, U. S. Department of Transportation (ex officio) A. E. JOHNSON, Executive Director, American Association of State Highway Officials (ex officio) ERNST WEBER, Chairman, Division of Engineering, National Research Council (ex officio) OSCAR T. MARZKE, Vice President, Fundamental Research, U. S. Steel Corporation (ex officio, Past Chairman, 1969) D. GRANT MICKLE, President, Highway Users Federation for Safety and Mobility (ex officio, Past Chairman, 1970) CHARLES A. BLESSING, Director, Detroit City Planning Commission HENDRIK W. BODE, Professor of Systems Engineering, Harvard University JAY W. BROWN, Director of Road Operations, Florida Department of Transportation W. J. BURMEISTER, State Highway Engineer, Wisconsin Department of Transportation HOWARD A. COLEMAN, Consultant, Missouri Portland Cement Company HARMER E. DAVIS, Director, Institute of Transportation and Traffic Engineering, University of California WILLIAM L. GARRISON, Professor of Environmental Engineering, University of Pittsburgh GEORGE E. HOLBROOK, E. I. du Pont de Nemours and Company EUGENE M. JOHNSON, President, The Asphalt Institute A. SCHEFFER LANG, Department of Civil Engineering, Massachusetts Institute of Technology JOHN A. LEGARRA, State Highway Engineer and Chief of Division, California Division of Highways WILLIAM A. McCONNELL, Director, Operations Office, Engineering Staff, Ford Motor Company JOHN J. McKETTA, Department of Chemical Engineering, University of Texas J. B. McMORRAN, Consultant JOHN T. MIDDLETON, Acting Commissioner, National Air Pollution Control Administration R. L. PEYTON, Assistant State Highway Director, State Highway Commission of Kansas MILTON PIKARSKY, Commissioner of Public Works, Chicago, Illinois CHARLES E. SHUMATE, Executive Director-Chief Engineer, Colorado Department of Highways DAVID H. STEVENS, Chairman, Maine State Highway Commission ALAN M. VOORHEES, Alan M. Voorhees and Associates

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Advisory Committee CHARLES E. SHUMATE, Colorado Department of Highways (Chairman) ALAN M. VOORHEES, Alan M. Voorhees and Associates WILLIAM L. GARRISON, University of Pittsburgh F. C. TURNER, U. S. Department of Transportation A. E. JOHNSON, American Association of State Highway Officials ERNST WEBER, National Research Council OSCAR T. MARZKE, United States Steel Corporation D. GRANT MICKLE, Highway Users Federation for Safety and Mobility W. N. CAREY, JR., Highway Research Board

General Field of Traffic Area of Operations and Control Advisory Panel G3-7 ALGER F. MALO, City of Detroit (Chairman) JOHN E. BAERWALD, University of Illinois WESLEY R. BELLIS, Consultant FRED W. HURD, The Pennsylvania State University ADOLF D. MAY, JR., University of California HAROLD L. MICHAEL, Purdue University KARL MOSKOWITZ, California Division of Highways WILBUR H. SIMONSON, Consultant WAYNE V. yOLK, Wisconsin Department of Transportation WILLIAM W. WOLMAN, Federal Highway Administration EDWARD A. MUELLER, Florida Department of Transportation

Program Staff W. HENDERSON, JR., Program Director M. MAcGREGOR, Administrative Engineer W. L. WILLIAMS, Projects Engineer W. C. GRAEUB, Projects Engineer HERBERT P. ORLAND, Editor J. R. NOVAK, Projects Engineer ROSEMARY S. MAPES, Editor H. A. SMITH, Projects Engineer CATHERINE B. CARLSTON, Editorial Assistant S . DH-404 Idaho Dept. of Hhwoys .. STANDARD. . COMPUTATION SHEET Description

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM REPORT 117

HIGHWAY NOISE A DESIGN GUIDE FOR HIGHWAY ENGINEERS

COLIN G. GORDON. WILLIAM J. GALLOWAY, B. ANDREW KUGLER, AND DANIEL L. NELSON BOLT BERANEK AND NEWMAN LOS ANGELES, CALIFORNIA

RESEARCH SPONSORED BY THE AMERICAN ASSOCIATION OF STATE HIGHWAY OFFICIALS IN COOPERATION WITH THE FEDERAL HIGHWAY ADMINISTRATION

AREAS OF INTEREST: HIGHWAY DESIGN ROAD USER CHARACTERISTICS URBAN COMMUNITY VALUES

HIGHWAY RESEARCH BOARD DIVISION OF ENGINEERING NATIONAL RESEARCH COUNCIL NATIONAL ACADEMY OF SCIENCES- NATIONAL ACADEMY OF ENGINEERING 1971 NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with NCHRP Report 117 their state universities and others. However, the accelerat- ing growth of highway transportation develops increasingly Project 3-7 FY '67 complex problems of wide interest to highway authorities. ISBN 0-309-01907-9 These problems are best studied through a coordinated L. C. Catalog Card No. 72-169279 program of cooperative research.

In recognition of these needs, the highway administrators - Price $4.60 of the American Association of State Highway Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it re- ceives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Highway Research Board of the National Academy of Sciences-National Research Council was requested by This report is one of a series of reports issued from a continuing research program conducted under a three-way agreement entered the Association to administer the research program because into in June 1962 by and among the National Academy of Sciences- of the Board's recognized objectivity and understanding of National Research Council, the American Association of State High- modern research practices. The Board is uniquely suited way Officials, and the Federal Highway Administration. Individual fiscal agreements are executed annually by the Academy-Research for this purpose as: it maintains an extensive committee Council, the Federal Highway Administration, and participating structure from which authorities on any highway transpor- state highway departments, members of the American Association tation subject may be drawn; it possesses avenues of com- of State Highway Officials. munications and cooperation with federal, state, and local This report was prepared by the contracting research agency. It has been reviewed by the appropriate Advisory Panel for clarity, docu- governmental agencies, universities, and industry; its rela- mentation, and fulfillment of the contract. It has been accepted by tionship to its parent organization, the National Academy the Highway Research Board and published in the interest of of Sciences, a private, nonprofit institution, is an insurance effective dissemination of findings and their application in the for- mulation of policies, procedures, and practices in the subject problem of objectvity; it maintains a full-time research correlation area. staff of specialists in highway transportation matters to The opinions and conclusions expressed or implied in these reports bring the findings of research directly to those who are in are those of the research agencies that performed the research. They a position to use them. are not necessarily those of the Highway Research Board, the Na- tional Academy of Sciences, the Federal Highway Administration, The program is developed on the basis of research needs the American Association of State Highway Officials, nor of the identified by chief administrators of the highway depart- individual states participating in the Program. ments and by committees of AASHO. Each year, specific areas of research needs to be included in the program are proposed to the Academy and the Board by the American Published reports of the Association of State Highway Officials. Research projects to fulfill these needs are defined by the Board, and qualified NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM research agencies are selected from those that have sub- are available from: mitted proposals. Administration and surveillance of research contracts are responsibilities of the Academy and Highway Research Board its Highway Research Board. National Academy of Sciences The needs for highway research are many, and the 2101 Constitution Avenue National Cooperative Highway Research Program can Washington, D.C. 20418 make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to (See last pages for list of published titles and prices) complement rather than to substitute for or duplicate other highway research programs.

FORlV RD This report will be of special interest to highway design engineers, highway planners, architects, tire manufacturers, automobile manufacturers, legislators, By Staff and other officials who have to deal with the problems of traffic noise. The research Highway Research Board presents information that will allow engineers and architects to predict noise levels expected from a new highway facility. By comparing these .predicted noise levels against recommended noise design criteria, the impact of highway-generated noise on the community can be estimated. The noise evaluation technique is presented by means of a series of examples and includes a "cookbook"-type manual. The recommended noise design criteria are based on task interference considerations of speech and sleep. It should be noted that these recommended noise design criteria (noise standards) are tentative and subject to change as additional research is undertaken.

Questions related to highway noise levels and their effects on users of adjacent property arise frequently in the planning and design of highway improvements, particularly in urban areas. It is important to have means of evaluating probable noise levels adjacent to highways so that noise may be considered in the design of highway features and reduced through legislative actions or enforcement of vehicle regulations, or by design changes. It was with these thoughts in mind that this research was initiated in 1963. How will the introduction of a new highway influence the noise environment? How acceptable will people living or working near the highway find this new environment? These questions are of increasing importance today, as both the number of highways and the number of vehicles on the highways increase. To enable the highway engineer to answer these questions, Bolt Beranek and Newman has developed a "Design Guide for Traffic Noise Prediction." The Design Guide, intended to be a design "cookbook" rather than an acoustical textbook, is com- pletely self-contained and makes generous use of coordinated worksheets, tables, and figures. In this way, the highway designer, with no experience in acoustics is at once able to use the Design Guide quickly and effectively. The Design Guide estimate of highway noise levels is built on information readily available to the highway designer. This information includes the characteristics of the traffic flow (traffic density, vehicle types, and speeds), the characteristics of the roadway (elevation or depression, surface roughness, steepness), and the characteristics of the observer (location, height, intervening barriers or planting). On the basis of these inputs, the designer obtains estimates of an average noise level and a peak noise level. The differences between the estimated highway noise levels and the criteria determine the impact of the highway on the neighborhood. When the estimated levels lie above the criteria, individual and even group reactions may occur, depending on how much the estimates exceed the criteria. If necessary, the designer can repeat the Design Guide procedure, introducing such changes as roadway relocation or depression or barriers in order to satisfy the criteria. The Design Guide thus not only equips the highway designer to take the noise of a new highway into consideration, but also shows how various alternate designs will produce different degrees of impact on the neighborhood environment. This effort was by no means designed to solve all of the problems in the field of highway noise, and additional highway noise research will be conducted under the NCHRP. Previously completed NCHRP studies involving highway noise are presented in NCHRP Report 78, "Highway Noise—Measurement, Simulation, and Mixed Reactions," and NCHRP Report 75, "Effect of Highway Landscape Development on Nearby Property"; legal problems involving highway noise are given in NCHRP Project 11-1(7), "Valuation and Compensability of Noise, Pollution, and Other Environmental Factors." Of the many facets of the highway noise problem, future studies should assess the effects of the temporal variations of highway noise on speech communications, sleep, learning, and mental health. In addition to the research contained herein, a "highway noise" tape recording has been produced to assist engineers in their understanding of how different noise levels are heard, what the significance is of changing noise levels by various amounts, and how motor vehicle noise varies with traffic flow conditions. Loan copies of the tape recording, "Illustrative Recording of Traffic Noise," are available on request to the NCHRP.

CONTENTS

I SUMMARY

PART I 2 CHAPTER ONE Introduction and Research Approach Definition of Symbols

3 CHAPTER TWO Findings Model of Traffic Noise Adjustments Criteria for Highway Noise

31 CHAPTER THREE Applications

31 CHAPTER FOUR Conclusions and Suggestions for Future Research Highway Traffic Noise Calculations Demonstration Project—Barriers and Propagation of Traffic Noise Attenuation Due to Structures and Intervening Buildings Tire-Roadway Noise Effects of Time-Varying Noise on Speech, Sleep, and Annoyance

33 REFERENCES

PART II

35 APPENDIX A Design Guide for Traffic Noise Prediction

75 APPENDIX B Illustrative Recording of Traffic Noise ACKNOWLEDGMENTS The study reported herein was conducted by Bolt Beranek undertaken jointly by Mr. Gordon, Dr. Galloway, and Mr. and Newman, Acoustical Consultants, in connection with Kugler. NCHRP Project 3-7. Cohn G. Gordon and Dwight E. Stewart Ferguson and Ronald Burns assisted in many of the Bishop acted as Co-Principal Investigators with major assistance field measurements of traffic noise undertaken during the study. from Dr. William J. Galloway, B. Andrew Kugler, and Daniel The measurement, analysis, and interpretation of stop-and-go L. Nelson. traffic was planned and directed by Charles Dietrich. David Lubman contributed to the statistical interpretations involved Analytic studies of traffic noise prediction procedures and in comparing traffic noise with ground noise and with speed. the review of noise criteria were largely accomplished by Particular thanks are due to Karl Pearsons, Dr. Sanford Messrs. Gordon and Nelson. The development of detailed Fidehl, and Brian Curtis for their efforts in preparing the design guide calculation procedures, tables, and graphs was highway noise demonstration recording. HIGHWAY NOISE

A DESIGN GUIDE FOR HIGHWAY ENGINEERS

SUMMARY Traffic noise is becoming an increasingly important consideration in the urban environment. Currently, traffic noise is the predominant and most widespread source of urban noise, and it is clear that in future urban planning the design and routing of new highways should include traffic noise as one of the parameters. This study has revolved about the need for a Design Guide that will allow highway engineers to include highway noise in the design of future highways. This report summarizes the technical considerations used in the calculation procedures and the design criteria given in the Design Guide that is part of this report (Appen- dix A). The report discusses and compares different analytical and experimentally derived models of traffic noise, and describes the model used in the Design Guide. The report also describes the sources of information and technical approaches used in determining the noise level adjustments for finite element length, acoustical barriers, elevating or depressing the roadway, gradients and different road surface conditions, and the presence of intervening buildings or foliage between the observer and the noise source. Finally, the report describes and compares several approaches to the selection of criteria for traffic noise. These include criteria based on comparison of intruding noise levels with background noise levels, task interference considerations such as sleep and speech interference, and annoyance. The Composite Noise Rating (CNR) procedures where community response estimates are made based on the characteristics of the intruding noise source, consideration of background noise levels, and assessment of some community factors were also investigated in conjunction with the criteria study. The final criteria selected for the design guide are primarily based on the consideration of existing background noise levels and on speech interference criteria. The report concludes by considering various future research needs. The Design Guide developed, based on this report, identifies an the variables necessary for traffic noise prediction in terms of roadway parameters familiar to highway designers, the intention being to provide an easy-to-use design "cookbook." These parameters are then identified for a particular traffic situation and, through a simple procedure, transformed into noise level estimates through the use of charts and tables. Special work sheets are provided to facilitate this procedure. The evaluation of the particular traffic situation is achieved by comparing the estimated traffic noise levels against design criteria. The design criteria provide "maximum" levels for a variety of situations and for both inside and outside use. An "Illustrative Recording of Traffic Noise" is provided to serve as an illustrative accompaniment to the Design Guide. The text of the recording appears as Appendix B. CHAPTER ONE INTRODUCTION AND RESEARCH APPROACH

Traffic noise is becoming an increasingly important parame- of the principles involved in their development. For this ter in the urban environment (1). Studies in several major reason this report includes a practical Design Guide for American and European cities have shown that despite the highway noise entitled "Design Guide for Traffic Noise noise produced by aircraft, surface traffic (automobiles, Prediction" (Appendix A). This Design Guide is the basic buses, trucks, motorcycles) is the predominant and most tool that has been developed in the study. Its purpose is to widespread source of noise. Even in industrial areas the allow the engineer to predict the noise environment of a dominant source is often the traffic related to the industrial highway design and to make decisions concerning the acceptability of this environment without recourse to other activity. As traffic activities increase, so urban (and suburban) than highway-related parameters. noise levels are generally on the increase. A recent survey A further accompaniment to this report is the "Illustra- of community noise (2) established the statistic that, in the tive Recording of Traffic Noise." In this recording some selected geographic areas, noise levels were apparently rising basic acoustic terminology is introduced and illustrated. The at a rate close to 1 decibel (dB) per year. This increase, ways in which a total traffic noise situation derives from a one might suppose, is directly attributable to the increasing succession of individual vehicles and the influences of traffic population on the roads. If this postulate is correct, various roadway and building designs on traffic noise are then it is clear that future urban planning that includes noise demonstrated. Finally, the recording demonstrates some as a parameter must pay close attention to traffic flows aspects of the impact of traffic noise on speech intelligibility. within the urban area. The text of the recording is given in Appendix B. Three general principles of noise control can be identi- The purpose of this report is to supply some indepth dis- fied as potentially applicable to the traffic noise problem. cussion of the procedures and data used in the Design The first of these is the direct control of the noise of the Guide. individual vehicle. The two major categories of motor ve- Chapter Two describes the various methods of predicting hicle that are acoustically significant are automobiles and and modeling traffic noise that were studied in the course diesel trucks. Automobiles, although individually quiet, exist of the program. The method used in the Design Guide is in such numbers as to make their total noise contribution developed and discussed. In addition, the types of adjust- significant. ments that are applied to the basic traffic noise prediction The second general principle of noise control concerns to account for road geometry and terrain effects (shielding, traffic routing. Through traffic can bypass populated areas; etc.) are discussed. The sources of data used in the Design the provision of limited-access highways can effectively re- Guide are given. Finally, various criteria by which the sub- duce the vehicle population on surface streets. Unfortu- jective effects of traffic noise on people and communitics nately, however, almost any highway routing must affect can be assessed are presented and discussed. The bases of some people. Highways often attract residential and semi- the criteria used in the Design Guide are given. residential developments around them, and so it must be Chapter Three indicates the aids developed for applica- anticipated that highways in non-populated areas may even- tion of the findings to highway design. In Chapter Four, tually find themselves the cause of environmental noise ,some conclusions deriving from the study are presented, and problems. future work is suggested. The third general principle of traffic noise control is that the highway design itself has an impact on traffic noise; DEFINITION OF SYMBOLS therefore, the highway engineer can exert some degree of control over the noise environment generated by his Al = articulation index. creation. C = speed of sound in air. This study is concerned with the last two principles and it D = distance measured between observer and near- revolves around the need for a design tool that will allow est point to center line of roadway, in feet. the highway engineer to include the noise environment as DB = distance measured between observer position one of the parameters in his highway design. Thus, this and barrier, in feet. study is concerned with formulating those aspects of traffic De = distance measured between observer and cut flow and highway design that influence traffic noise and of roadway, in feet. relating these to the environmental needs of those people = distance measured between observer and who might be exposed to highway noise. Of overriding equivalent lane of roadway, in feet. concern in this study has been the need to develop these = distance measured between observer and the formulations so that they can be used and appreciated by DF center of the farthest lane of roadway, in feet. the highway engineer without any in-depth understanding D = distance measured between observer and cen- S = speed measured as the average speed of ve- terof hicular flow, in miles per hour. = distance parameter, measured between ob- SA = speed measured as above, for automobiles. server and shoulder of roadway, in feet. ST = speed measured as above, for trucks. U = level that describes effects of voice level and T = spacing between consecutive vehicles, in feet. speaker-listener distance. V = vehicle volume, in vehicles per hour. H = height parameter, in feet. VA = vehicle volume parameter (in vehicles per L = length measured along a finite roadway ele- hour), for automobiles only. ment, in feet. VT = Vehicle volume parameter (in vehicles per La = instantaneous traffic noise level measured in hour), for trucks only. dBA. X, Y, Z = random variable. Laio = sound level that is exceeded 10% of the time. Xo, Y0 = mean level. La50 = sound level that is exceeded 50% of the time. o = angle measured as included angle between ob- Lp = peak traffic noise level measured in dBA. server and roadway element. N = number of traffic lanes on roadway. H = source power per unit length. p = acoustic pressure. p = traffic density, in vehicles per mile. (p2 ) = mean square acoustic pressure. Poc = characteristic impedance of air. P = width parameter, measured from outside to a- = standard. outside lane on roadway, in feet. a-2 = variance.

CHAPTER TWO

FINDINGS

MODEL OF TRAFFIC NOISE The following sections discuss examples of some of the methods used in developing highway noise models, compare A vital part of the Design Guide is the methodology the results of these analyses, and present the bases for the whereby the noise environment produced by a specified method of predicting traffic noise that is used in the Design traffic situation is predicted. This section presents the stud- Guide. ies and thoughts behind the prediction methodology so that concepts and limitations of the methodology can be clearly appreciated. Requirements Past efforts to describe quantitatively the noise generatcd At the onset it is important to define just what the output by freely flowing traffic have taken two basic approaches: of a prediction method must consist of. From measured acoustical data obtained from arn- First, the noise output should be specified in terms of an pling traffic flows, attempts have been made to find mathe- easily measurable physical descriptor of the noise. Past matical expressions that most nearly describe the observed studies of response (3, 4) to traffic noise have shown that noise levels as a function of the several traffic flow parame- several different scales of physical noise measurement cor- ters (e.g., speed, vehicle flow rate, and observation distance). relate well with subjective response to noise. Such scales From knowledge of the acoustic power generated by include various versions of noisiness, loudness, and A- typical individual vehicles, noise models have been derived weighted sound pressure level. The latter scale is particu- by superimposing the sources that constitute the total flow. larly useful because A-levels can be read directly from any Three techniques used in this regard are: (I) assuming the precision sound level meter. Because the "dBA" level is total acoustic power due to all vehicles to be distributed regarded as (3) "statistically indistinguishable from the best uniformly along a continuous line and thus constituting an psychological derived measures in its reliability as a pre- acoustic line source of known acoustic power per unit dictor of human response to traffic noise" it is increasingly length; (2) considering the vehicles to be uniformly spaced being specified in national standards, and recommended in discrete sources along a hypothetical single-lane-equivalent international practice, for traffic noise studies. It is the roadway; and (3) using a Monte Carlo simulation pro- physical measure, therefore, used in this study. cedure, and deriving the statistical expectation of noise A second requirement for the prediction method con- produced by a randomly occurring flow of vehicles along cerns the way in which it accounts for the statistical varia- a hypothetical single-lane-equivalent roadway. tion in traffic noise from moment to moment. Early in this study it was decided that a useful prediction method must of the statistical distributions are controlled by individual define at least two points on the "statistical time distribu- noisy vehicles and by background (ambient) noise sources, tion" curve of the noise levels, and the points selected were respectively. Furthermore, for sufficiently long measure- the 50% level (L50), defined as that level exceeded 50% ment sampling times, it was found that noise level distribu- of the time, and the 10% level (L10), defined as that level tions are statistically "normal" with time for the flow rates exceeded 10% of the time. between 400 and 2,250 vph observed in the study. A third requirement relates to the characterization of the The effects of average vehicle speed, S, were studied. It sources of traffic noise—the vehicles themselves. On most was found that for fixed values of the ratio, V/ D, in which highways the vehicle population can be divided into two V is the flow of vehicles per hour past the observation acoustically significant groups. The first group can be de- position and D is the distance from highway center line to fined as "automobiles" and consists of gasoline-fueled ve- the observer, noise levels varied as 30 log S. Because the hicles having the general operating characteristics of pas- noise levels due to a moving column of noise sources can senger cars. The second group covers heavy diesel-fueled be shown to vary as 11S, the source strength of the indi- trucks such as tractor/trailer combinations and tank trucks. vidual vehicles in the Johnson and Saunders model is seen Certainly there are some vehicles that do not clearly lie to vary as the fourth power of speed. This is further within either of these two categories. Their numbers, how- discussed later. ever, are sufficiently small as to render them acoustically Taking account of the several factors just mentioned, insignificant—for highway design. Johnson and Saunders have produced the following em- Thus, the prediction method must be able to handle pirical expression for predicting the mean noise levels, in traffic situations involving different mixes of automobiles dBA, due to traffic flow on a level roadway: and trucks, each traveling at a different average road speed. L50 =3.5+101ogV—101ogD+3OlogS (1) Thus, it was decided early in the study to develop a prediction method for each vehicle group separately and to In the data from which Eq. 1 was derived the over-all arrive at the composite traffic level by summing the vehicle composition was normalized to include 20% com- contribution from each group. mercial vehicles such as trucks. Thus, the empirical expression is assumed valid for this mixture of vehicle types, Empirically Derived Model varying ±1 dB with a mix ranging from 0% to 40% trucks. The objective in the empirically derived model is to infer The speed range considered was from 33 to 55 mph, with from measured data the parametric dependences that relate the constant in Eq. 1 obtained by normalizing to 40 mph. traffic noise levels to the physical measures of the traffic The small effect of trucks on the mean noise levels is not flow. Empirically derived models of traffic noise are limited at all consistent with observations in the United States (3). to the extent that data are available for the appropriate These results may be compared with Galloway's linear- range of traffic conditions and to the extent that effects not ized approximation to the Monte Carlo simulation of traffic related to traffic noise (spurious noise sources, attenuation, noise [described by Galloway et al. (3) and in the follow- etc.) can be discerned in the data. ing]. This approximation expresses the mean noise level in An important study of freely flowing traffic noise was dBA as: produced in Great Britain in 1967. Johnson and Saunders L5o=20+ 10logV-10logD+20logS (2) (5) undertook a series of roadside noise measurements between 1963 and 1965 and, on the basis of the resulting data Comparing the numerical values obtained from the two and theoretical considerations, derived a model of the noise equations for D = 100 ft, S = 40 mph, and V = 1,200 vph, for freely flowing traffic. Efforts were made to ensure that one obtains 62.3 dBA and 62.8 dBA, respectively. This is measured data did not include anomalous effects due to indeed a strikingly close agreement if the small effect of the shielding, reflective surfaces, and the like. Noise levels, in truck-passenger car mix in Johnson and Saunders data is dBA, observed under various conditions of traffic flow, considered not representative of situations in the U.S. It velocity, and observation distance were examined with a is estimated that for a 20% mix of diesel trucks the average statistical distribution analyzer to determine the time dis- noise level would be 8 dBA higher than that predicted tribution of noise levels. Different parts of the level dis- previously (3). tributions were studied as the several traffic parameters varied. Analytical Models As might be expected, the results of the study show that Continuous Line Source Model at distances close to the roadway, and/or at sufficiently low traffic densities, it is the noise of individual vehicles that is The simplest model for freely flowing traffic noise assumes observed, and noise levels decrease at 6 dB per doubling of that vehicles are spaced sufficiently close together that the distance as expected for discrete (point) noise sources. At total acoustic power can be considered evenly distributed greater distances from the roadway and/or higher traffic along the equivalent center line of the roadway; Thus, the densities, the noise due to individual vehicles tends to smear source strength is described in terms of constant power per out into a line source from which levels (mean and peak) unit length. To a first approximation the line source is decrease at 3 dB per doubling of distance. assumed to be infinite in length and the expression for the Another result of the Johnson and Saunders study is that, acoustic pressure, (p2 ), at the observation point (Fig. 1) as would be expected, the highest and lowest noise levels due to an element, dx, of the line source, as follows:

Figure 1. Schematic configuration for derivation of line source noise model.

model was found to be accurately described by a Gaussian d6 (3) (p2)= (_podH)2i-D time-level distribution, the single line source model has no in which II is the source power per unit length, D is the statistical time distribution of levels. If one is interested perpendicular distance from the observation point to the not only in the mean levels that are presumably described by Eq. 5, but also, say, in the 10% or 90% levels, some roadway centerline, and p0c is the characteristic impedance of air. It should be noted from Eq. 3 that the contribution measure of a statistical time distribution must be introduced, to the mean-square acoustic pressure is a linear function of which in reality results from the truly discrete nature of the the subtended angle, d9. Segments of the line source that vehicles that constitute the traffic flow. correspond to equal angles of intercept contribute equally to the total mean-square acoustic pressure. Discrete Source Model Integrating Eq. 3 from limits of —7r/2 to +7r/2, cor- As mentioned, Johnson and Saunders have derived in con- responding to an infinitely long line source, the total junction with their empirical model a simple theoretical acoustic pressure is given by model of highway noise based on assumed uniform spacing p0c111 of identical vehicles, all traveling at the same average speed (4) D 2..- on a single-lane straight roadway. The spacing between consecutive vehicles is taken to be T, the average speed is Considering the vehicles to be automobiles and using the 5, and the perpendicular distance from the roadway to the automobile source power suggested by Galloway et al. (3), observation point is D. the noise level due to an infinite line source can be expressed The acoustic intensity observed is the summation of an in the following manner: infinite series of terms, each of which is proportional to the L50 =20+ 10logV-10logD+20logS (5) inverse square of the distance of the individual sources from the observation point. Thus, which is identical to Eq. 2. Thus, a simple continuous line source model is sufficient to estimate the average traffic 1 =-° (6a) noise level if the flow rate is of the order of 1,000 vph or 1=+ D2 + (St+nT) 2 more. It should be noted that by assuming a line source in which t is time from an arbitrary reference and n is a free of even vehicle distribution per unit length, the noise levels index to identify the individual vehicles. described are steady with time. Whereas the empirical This summation can be replaced by the single term, rl

sinh(2,rrD/T) L50 =4O log S— lO log D+ lO log p (6b) 3dBA (14) [ cosh(2D/T) - cos (2St/T)] -I- 10 log [tanh(1.19 X 10 3pD) ] + K Substituting this into Eq. 3, the intensity can be defined For sufficiently large values of the quantity DI T (pD> (within a factor representing the individual source power) —1,200), the hyperbolic tangent term approaches unity and as a function of time. The value of t is arbitrarily set equal the logarithm of the hyperbolic tangent vanishes. The high- to zero when a particular vehicle (n = 0) is at nearest density flow regime then tends to the same dependence as approach to the observation point. derived in the empirical model (see Eq. 1): Clearly, the maximum intensity is obtained when the L50 =K3 ±l01ogV-101ogD+30logS (15) cosine term in the denominator of Eq. 6b equals +1 (vehicle at nearest approach) and the intensity has its mini- The time-varying nature of the cosine term in Eq. 6b mum value when the cosine term equals —1 (two nearest indicates a variation in noise level around a mean value, as vehicles equidistant from the observation point). The 50% compared to the steady level prediction of the simple line level (i.e., the level exceeded for 50% of the time) coincides source of Eq. 5. A probability density function for the with the cosine term equal to 0. The mean level can then be noise level distribution described by Eq. 6b could be devel- written as oped. The periodicity introduced by the cosine term, however, would generate a non-Gaussian distribution that is L10 — lO log _.tanh(21rD/T)] (7) not observed in the data obtained in traffic noise measure- DT I ments. In practice, therefore, only the mean level predicted and the maximum level can be expressed as by this approach is of use.

Lmax - 10 log Icoth (1rD/T)] (8) Simulation Model The analytical models described previously have several Noting that approximations can be made to the hyperbolic drawbacks. First, traffic flow is not characterized by uni- tangent and cotangent functions over certain ranges of the form spacing of vehicles. Second, the absorption of sound arguments, one sees that for DIT> ¼ (pD = 1,320 in the atmosphere is a function of frequency and distance, ft-veh/ mile) neither being accounted for in the analytical models. Third, the identification of a "siiigle-laiie equivalent" for L50 —10 log (l/DT) (9) multi-lane highways is justifiable only after examination of the effect of assuming multiple lanes first in the analysis. and for D/T < Yi (pD <440 ft-veh/mile) Fourth, the simple models do not allow for mixture of L50 —lO log (11T2 ) (10) various vehicle classes based on the noise output of the different types of vehicles. Fifth, the statistical distribution 2,640 ft-veh/mile) Similarly, for DIT> ½ (pD> of noise levels as a function of time cannot be realistically Lmax ~ 10 log (1IDT) (11) obtained from a deterministic model. Galloway et al. (3) used a simulation model to account and, for DIT < 1/6 (pD < 880 ft-veh/ mile) for these factors in developing a model of noise levels produced by freely flowing traffic. The model assumes a log (1ID2 ) (12) L.a. ~ 10 random distribution of vehicles distributed along a highway Note that to this point the results of the discrete source of any number of lanes. The noise characteristics of each model are independent of the type of vehicle, with all vehicle class are described in terms of octave frequency vehicles being assumed identical. band sound pressure levels at a given reference distance. To introduce the power dependence of each individual The simulation consists of summing the noise levels pro- noise source, Johnson and Saunders have indicated that duced at a specified observation point by a Poisson distri- each automobile generates acoustic power proportional to bution of vehicles having an average flow rate of 111. By the fourth power of the vehicle's speed (5). This velocity repeating the process a number of times, each time ran- dependence is assumed "on the basis of a statistical sam- domly selecting the vehicle distribution, but maintaining the pling of traffic cruising on an uninterrupted highway and average flow rate constant, histograms of the noise level as assumed representative of average vehicle behavior." Thus, a function of time are generated for a particular set of each term of the summation in Eq. 6a should contain the average flow rates, lane configurations, and vehicle mixes. factor K1S4, in which K1 is a constant. The mean noise The histograms allow computations of both mean noise level would then show the dependence, or levels and measures of the distribution function (e.g., standard deviation) for the various traffic flow parameters. L50 =4O log S— 101ogD — lO log T A detailed discussion of this approach is available by + 10 log [tanh(.-)] + K2dBA (13) Galloway et al. (3). It should be noted that the model successively superimposes vehicles until the addition of one more unit causes the summation to increase by no more in which K2 is a constant derived from experimental data. Because the headway distance, T, is inversely proportional than some specified amount (e.g., ½dB). In this sense, to the number of vehicles per mile, p, Eq. 13 can be re- the computer model truncates the roadway at some distance written as beyond which the individual traffic noise sources are in- WI significant with regard to the total effect of all closer technique is that noise levels can be estimated for traflic vehicles. The computer simulation, then, never describes flow conditions that may not be presently available or easily an infinite array of vehicles but always sees a finite road- accessible for measurement. TrallIc mixes, road geometries, way length. flow densities, and velocities can be varied at will. Some typical data derived from the simulation model are shown in Figure 2. As part of the study by Galloway et al. Comparison of Models the results of the computer model were verified by com- All the different models described previously contain terms parison with measured data; agreement was found to be that are linearly dependent on flow velocity, V, and dis- excellent (3, Fig. 1). An important asset of the simulation tance normal to the roadway, D. These terms describe the

80 0

1, 55

PASSE NGER CARS ONLY 20mph O 35mph 50mph o 65mph

40 - _

35 1 1 10 100 1000 Density in Vehicles per Mile of Roadway Figure 2. Traffic noise levels from computer simulation 100 ft from single-lane equivalent flow. line source characteristic of highway noise. The discrete At very high traffic densities, the computer model source model of Johnson and Saunders, Eq. 14, also in- implies that mean noise levels increase with density at a cludes the term 10 log [tanh (1.19 X 10 3pD ) 1, which ef- rate that is less than linear (i.e., more nearly 6 log p than fectively adjusts the line source representation to account 10 logp). for discrepancies between the lumped and distributed source Simulated noise levels decrease with distance at a rate descriptions. This effect is most marked at low densities that is greater than the linear expression 10 log D. The and! or small observation distances and approximations to computer-generated mean noise levels for distance of 100, the hyperbolic tangent function were introduced previously. 300, and 1,000 ft from the roadway more nearly approxi- At higher values of the product, pD, the hyperbolic tangent mate 15 log D than 10 log D behavior. term vanishes and the discrete source model approaches the An explanation for the behavior of the simulation result line source description. lies in the method by which the simulation model truncates A significant theoretical difference between the Johnson the infinite linear array of vehicles assumed in the other and Saunders results and the other models is the velocity formulations. The computer randomly positions successive dependence used. In their results, the effect on noise level four-vehicle units along the roadway in accordance with of individual vehicle velocity, obtained from random sam- the design traffic mix and traffic flow density. This process ples, was chosen to vary with the fourth power of velocity. terminates when the addition of another unit increases the In this work passenger-car noise varies with the third cumulative sound pressure level by less than a specified power of velocity, based on controlled measurements of the amount. A simple analysis that parallels the mechanics noise produced by individual vehicles. performed by the computer suggests that, as the traffic It might be argued that the acoustic power generated by density increases and noise levels increase, the length of the individual passenger vehicle should be proportional to highway that is effectively included in the view of the the power expended by the vehicle, thus providing some computer to obtain a stable noise distribution decreases. physical justification for selecting the cubic dependence on One can examine the practicality of the foregoing result. velocity. It is likely that the actual behavior observed is Considering the distance dependence of simulated traffic related to the predominance of exhaust, engine, or tire- noise levels, one notes that in the calculation for a finite roadway source mechanisms. Further, the importance of length line source, the noise level is proportional to the each mechanism probably varies not only with the type of angle, O where vehicle, but also with the speed range of intetesss. This is notably important as regards trucks because these vehicles O=arctan (L/2D) (16) tend to operate at nearly constant engine speeds and use L being the line length shown in Figure 1. Expanding the gear changes to regulate velocity. In a practical sense, the arctangent function in powers of the argument, (L!2D), difference between third- and fourth-power velocity laws is for L greater than 2D, it is seen that only when the value not very significant in the numerical results for the velocity of L!2 is much greater than D can the angle be approxi- range of practical interest. This is shown by the excellent mated by the first term of the expansion, /2. In this case agreement between the models described in the example the result is equivalent to the infinite line source result of given previously in "Empirically Derived Model." Eq. 13. The simple analysis of the finite line source further Because the velocity term in each of the models is a indicates that distance behavior should vary from 10 log D measure of the acoustic power produced by the individual to 20 log D as the ratio, L/2D, varies from very large to vehicles that comprise the traffic flow, the parametric models very small as compared to unity, respectively. The simu- given previously can be generalized to any type of vehicle lation results given by Galloway et al. (3) are closely by replacing the velocity terms of models 1, 3, or 4 by the described by the term 15 log D. The question then is, appropriate description for the type of source concerned. "Is the distance effect a realistic phenomenon or is it an In the development of the estimation procedure for use in idiosyncrasy of the computer procedure?" A series of measurements were obtained to compare with the simulation the Design Guide, it is assumed that automobiles generate results. The distance dependence characteristics in the two acoustic power proportional to the third power of their cases agree very closely. This leads one to believe that, in speed and that truck noise levels are independent of speed real life, roadways with which one is usually concerned are over the major portion of their operating range. indeed truncated at such lengths that the near-field approxi- Comparing now the results of the computer simulation mation (one-term expansion) to the arctangent function of• model with the empirical and theoretical models, very good Eq. 13 is not realized. As an example, one might look for agreement is obtained between the line source model and the configuration in which the noise level calculated by the the computer simulation output over the intermediate range two-term arctangent expansion is 1 dB below the infinite of traffic densities and for fixed observation distance, D. line value. This condition is obtained when L = SD, or the At lower traffic densities, the simulated levels are accurately double angle, 20, equals 136°. described by the discrete source analytical model. The in- It seems likely that in many practical situations the creasing slope of the plots in Figure 2 with decreasing length of roadway that effectively contributes to the noise density is accounted for by the hyperbolic tangent term of levels observed at a particular point is less than five times the analytical model. the observation distance. Lt is thus appropriate to expect Two interesting effects appear in the computer model noise levels to fall off at more than 3 dB per.doubling ..of that do not agree with the analytical and empirical models: distance from the roadway. This effect is both geometric

(i.e., shielding of extremities of the roadway by buildings final constant, as the means of predicting, for the Design and terrain) and physical in terms of the reduction in noise Guide, the average noise levels of automobile traffic. The levels produced by distant sources as a result of air absorp- modified equation is tion of sound. L50 = lO log p - l5 log D + 30 logS On the basis of the explanation for the distance behavior +10 log [tanh(1.19 X 103pD)] + 29dBA (19) demonstrated by the simulation model and on the strength of measured data, it is believed it is more appropriate to or, in terms of the more conventional automobile volume describe highway noise levels by 15 log D rather than by flow, V (vehicles per hour), This adaptation should apply only to the traffic 10 log D. L50 = 10 log V— 15 logD +1ogS flow regime over which the line source description is appro- 10 3VD/S) I + 29dBA (20) priate. The corresponding effect of line truncation with + 10 log [tanh(l.19 X regard to the discrete source noise model is to limit the This equation is plotted in Figure 3 for a fixed distance of summation of Eq. 6a to finite values of n. It is gratifying 100 ft from the traffic lane and for different values of aver- to note that the results of the computer simulation model age automobile speed, SA. This figure appears as Figure have brought attention to certain aspects of traffic noise that B-3 in the Design Guide (Appendix A). * are observed in reality, but that have seemingly escaped It should be noted that the foregoing model considers all consideration in previous analytical modeling techniques. traffic to be traveling on a single lane at a distance, D, from Incorporation of these modifications into the model of the observation point. In a later section the method of traffic noise for use in the Design Guide are discussed in extending the model to account for the distribution of the the following. traffic population on a number of parallel lanes is discussed.

Automobile Traffic Prediction Truck Traffic Prediction It has been noted that over a wide range of traffic flow Rather than extend the automobile noise prediction method situations the computer simulation results of Galloway et al. to account for different (non-zero) percentages of heavy (3) show good agreement with measured data. With the trucks, it is more convenient to consider trucks as an en- exception of the decreased density dependence at very high tirely different population of vehicles an4 tQ develop sepa- traffic densitics, it seems appropriate to model the noise of rate prediction curves that apply only to trucks. The real automobile traffic for closeness of fit to these simulated traffic situation that is a superposition of the automobile and levels. truck populations is then established simply by adding The problem then is to bring about agreement between logarithmically the predicted noise levels of each popula- the analytical models and the simulation model for various tion, because each population is statistically independent of values of traffic density and velocity at a standard distance the other. (in this case, 100 ft). For values of pD > 600 ft-veh/ mile With regard to noise levels due to truck traffic, many one finds that the line source model described by of the physical arguments and basic models are identical to the development of the automobile noise prediction L50 =101ogp—l5logD+3OIOgS+29dBA (17) schemes. The analytical model of Johnson and Saunders is is in excellent accord with the curves of Figure 2. For developed independently of the type of source vehicles, with values of pD <600 ft-veh/ mile, very good fit to the curves the source characteristics inserted. The empirical model of of Figure 2 obtains from Johnson and Saunders is based on mixed automobile and truck traffic flows of 20% truck composition; therefore, L50 = l0 log p - l5 log D + 30 logS this model is probably not particularly applicable to the + lO log [tanh(1.19X 10 3pD)]+31dBA (18) study of noise due to trucks alone. The line source model which derives from the analytical model for uniformly developed with regard to automobile traffic includes third- spaced discrete noise sources whose source power and power velocity dependence of the individual sources that generalized spectrum are given by Galloway et al. (3, compose the line source. Clearly, the line source model, Fig. B-7). Note that when the product, pD, exceeds 1,320 Eq. 17, and the discrete source model, Eq. 18, readily lend ft-veh/ mile the logarithm of the hyperbolic tangent term themselves to modification for the generalized truck source approaches zero and the parametric dependence of Eq. 18 characteristics. is identical to the line source model. The difference between As noted previously and as discussed by Galloway et al. high-density noise levels predicted by the two methods is a (3), truck noise levels are nearly independent of velocity. constant 2 dB. Comparing the low-density (pD < 600) Furthermore, it is observed that the noise levels due to a levels described by Eq. 18 with the computer simulation, truck at 50 ft exceed the noise due to the average auto- one finds best agreement at 50-mph velocity. At higher mobile, at the same distance and traveling at 50 mph, by velocities the analytical model overestimates the computer about 15 dBA. One can, therefore, modify the models by results by 1 to 2 dB; at speeds less than 50 mph the ana- dropping the 30 log S term from each formula and finding lytical results are slightly lower than the simulated noise an appropriate constant by comparison with the estimated levels. automobile noise levels at fixed values of p and for values Because the generally important range of traffic densities of S and D of 50 mph and 50 ft, respectively. is described by the condition, pD> 600 ft-veh/mile, the For truck traffic the general expression for the mean researchers have selected Eq. 18, with an adjustment of the noise level can be written vo? +ha+, io LOS S 1-o pi+ 3 $ ue'j here 10

80 50 40 30 70

SA mph

40 DN = 100 FT

20 Hourly Auto Volume, VA - vph Figure 3. Plot of Io for automobiles as a function of volume flow and average speed.

L50 =101ogp—l5logD+K (21) totes to the same parametric dependence as the line source model at sufficiently high values of the product, pD, there Evaluating this at D = 50 ft, S = 50 mph, and equating to being a 2-dB difference between the levels predicted by the Eq. 17 plus 15 dB, the value of the constant, K, is found two different methods at high densities. to be 95 dBA. Thus, the level of truck traffic noise is In the Design Guide the modified equation that follows predicted by is used to predict the mean noise levels due to truck traffic only: L50 = 101ogp — 15logD+95dBA (22) L50 '= 101ogp — lSlogD By a similar procedure, one can relate the discrete source + 10log[tanh(1.19X 10pD)]+95dBA (24) noise model for trucks to the similar expression for auto traffic to find the general equation or, in terms of the truck volume flow, V,

L50 = 101ogp — 15logD L50 = 101ogV — 101ogS — lSlogD +10log[tanh(1.19X 10 3pD)]+97dBA (23) + 10log[tanh(1.19X 10VDIS)]+95dBA (25) Because no data are available for noise levels due to This equation is plotted in Figure 4 for a fixed distance of 100% truck traffic, no direct check is possible to verify the 100 ft from the traffic lane and for different values of results of the foregoing equations. By analogy with the average truck speed, S. Note the apparent paradox that situation for automobile traffic, it might be anticipated that truck traffic noise at fixed volume flow decreases with in- Eq. 22 would best describe high-density truck flow (where creasing vehicle speed. This is accounted for by the fact the line source model is appropriate to significant vehicle that truck traffic noise is a function of vehicle density only overlap), whereas the discrete source model should better —distance being constant—and that, for fixed volume flow, fit observations of low-density truck traffic noise. As in the density decreases as average speed increases. Figure 4 case of automobile noise, the discrete source model asymp- appears as Figure B-4 in the Design Guide.

100

DN = 100 FT 60

20 30 50 40 50 60 70

I I I I I III! I I I I I I liii 10 100 1000 10,000 Hourly Truck Volume, VT - vph Figure 4. Plot of L. for trucks as a function of volume flow and average speed.

Effect of Road Width and Observation Distance must be taken of the width of the roadway occupied by traffic. So far, all the models and prediction equations have as- Account must also be taken in the real situation of sumed that the traffic is located at a distance, D, from the changes in the distance between the observation position observation position. In real life, of course, a highway may and the roadway. This matter is discussed earlier; suffice it have many lanes, and the width of the roadway may be here to say that a 15 log (DE) relation has been selected such that the observation distance from the near lane is as representing most closely the rate at which levels change significantly different from the observation distance from with distance from a roadway in real life. the farthest lane. The two influences of roadway width (or number of This problem can be overcome by using the concept of lanes) and observation distance are taken into account by the "single-lane-equivalent" distance. This is defined as applying to Figures 3 and 4 the corrections shown in that imaginary lane on which the total traffic flow can be Figure 5. The relevant observation distance is taken to be assumed located to be acoustically identical to the real-life the distance to the center line of the near lane (DN). This situation. This distance is denoted by DE in this report and seems to be appropriately convenient. Figure 5 appears as it can be shown to approximate closely to the geometric Figure B-5 in the Design Guide. mean of the distances from the observation point to the Two special effects are not taken into account in Figure nearest (Dr) and farthest F) lane center lines, respec- (D 5. Firstly, for sufficiently low-density traffic flow (pD < tively; i.e., 1,320 ft-veh/mile), distance behavior of mean noise levels D, but also on DE =VDN DF (26) is dependent not only on the term, 15 log the term, 10 log [tanh(l.19 X 10 3pD)}. For values of The prediction curves of Figures 3 and 4 in assuming all pD <420 ft-veh/ mile, it can be shown that the hyperbolic the traffic to be located on a single lane imply the use, tangent tends to the value, 1.19 X 10 3pD, which effectively therefore, of the single-lane-equivalent concept and, in reduces the distance dependence to —5 log D. This result applying these curves to a real traffic situation, account is not shown in that the reduction in slope of any one of 12 Mill IN on IUllhlUI11111I _JHHhIRIIIIlIIIUUIIIIIII __uiiuiouIauuIIIllhIUuIuIuII UiiUUIIIIIIIhUhIIIIII "Ui!iiiIIIIIIllhRUIIIIIII I INI, uIIIIIIINlNhIIH F Ro dw.y Width milli I ,uiiiiiiIuiIIuvsuaIaIIuI __•iilIIIIIUUUIIIIIIIIIIIII iiiiIUIIIIIIIIi!IRIIlIIIII Mill ONhhhhhhh1hI millillinsom llillooLillillII ._!11111I!11111111111u111Il Figure 5. Distance adjustment to account for observer-near lane distance and width of roadway.

the curves of Figure 5 would be related to the product, pD, is also required. Early in this study it was decided that the rather than simply distance alone. noisier aspects of the traffic environment could be ade- Secondly, it can be shown that sufficiently close to quately defined using the 10% level, L10 (i.e., that level a multi-lane highway the single-lane-equivalent concept which is exceeded for 10% of the time). In this section breaks down in that levels do not fall off as from a finite the method by which L10 can be estimated is described. or infinite line source but rather are influenced by the Using the theoretical model of Johnson and Saunders the depth-of-field of the distributed source. The net result of 10% intensity level can be evaluated by suitably setting the this phenomenon is to further reduce distance dependence value of 27rSt/ T in Eq. 6b. The appropriate value of the of the noise levels. Unlike the geometric effect involving cosine term is 0.951. The difference between the 10% and the traffic flow density, this latter modification to the 50% levels can, therefore, be written D (assumed) 15 log D behavior is a function solely of the distance from the source and the true physical extent cosh(l.19 X 10pD) L10 —L50 (27) (depth) of the source. — 10 log cosh(1.19 X 10pD) —0.951

Computing the 10% Level Because this model is based on a regular array. of moving vehicles it must be expected to be in some error insofar as Knowledge of the average traffic noise level is not, in itself, the "tails" of the statistical time distribution are involved. necessarily sufficient if one is to define environmental acceptability. Some knowledge of the environmental peaks At low values of pD, however, where there is no "overlap" 13

of source influence, Eq. 27 should begin to approximate decibel adjustment to give the 10% level for both auto- the truth. mobiles and trucks. A source of data concerning the 10% traffic noise level Step 5: Using the usual decibel addition techniques, is to be found in Galloway et al. (3) from the simulation combine the 50% levels and the 10% levels for auto- model results; standard deviations for 100% automobile mobiles and trucks to obtain the 50% and 10% levels of traffic at different distances and volume flows are shown the composite vehicle population. (3, Fig. 6a). These data collapse to a single curve if plotted against the parameter pD (ft-veh/ mile). If it is assumed ADJUSTMENTS that the statistical time distribution is approximately normal, then the difference between the 10% and 50% levels The basic traffic noise model assumes a straight, infinitely is found by multiplying the standard deviation by 1.28. long roadway lying at grade on a flat, level terrain. Apart This approach has the two following weaknesses: from the flow parameters the only variables included so far are roadway width (number of lanes) and observer-near 7 1. The assumption of distribution normality is not cor- lane separation. rect at low values of pD. To accommodate such real-life idiosyncrasies as curves, 2. At high values of pD the standard deviation might not junctions, gradients, cross-sectional changes, and non-level

Vertical Adjustment fraction; an acoustic barrier does not create an absolute acoustic "shadow" on the side of the barrier remotc from The vertical displacement of an at-grade roadway to a posi- the source—diffraction of the sound at the top edge of the tion below (depressed) or above (elevated) ground level barrier "spills" sound energy into the shadow zone. provides a certain degree of acoustic shielding of the Consider the schematic diagrams in Figure 7 in which vehicular noise sources from the observation position. the elevated and depressed highway configurations are• The theoretical and experimental performance of acoustic represented by a source and an observer separated by a shields or barriers has been discussed by several authors knife edge. In the case of the elevated configuration, (a), 9). The basic principle involved is that of dif- (1, 3, 8, the position of the knife edge corresponds to the outer edge of the shoulder; in the case of the depressed configuration, (b), the knife edge corresponds with the intersect of the cut-slope with the terrain. In (c) the generalized geometry is shown represented by dimension X, Y and 7. TABLE 1 In a recent theoretical and experimental paper by ADJUSTMENT FOR INCREASED NOISE LEVEL Maekawa (8), the performance of semi-infinite acoustic OF TRUCKS ON GRADIENTS shields as a function of those parameters was carefully

GRADIENT ADJUSTMENT discussed and validated in the laboratory. The basic design (%) (cIa) curve deriving from Maekawa's study is shown in Figure 8. It relates the excess attenuation of a semi-infinite barrier 3to4 +2 to the parameter 8(X + Y - Z) and the wavelength of 5to6 +3 the radiated sound; however, Maekawa's model applied +5 only to a single source-receiver distance. To obtain design data for practical use in highway design, Galloway (3) ,Theuence of gradients of 2% or less is considered to be neglible.

___II!IIiiIIIIIIII__ 11111111 11111111 ___IIINI!!iIIII 11111111 _11111111 ___IIIIIIhhiI!iiii!IIIIIII_ 11111111

IIIIIHIIIIIIIIIiIIEINiIIIIHI104 1 o6 102 - 103 io VD/S In fs.t - v.hlcks/mIIe

Figure 6. Derivation of 10 - Lo for homogeneous traffic population. ç k 15

performed measurements of noise produced by traffic under Source conditions of elevated and depressed grades. Based on these measurements Maekawa's curves were modified to be linear, as shown in Figure 8. This curve forms the basis I Observer for the adjustments for vertical configuration used in the Design Guide under the following assumptions; The design curve is applicable to a lane of vehicles (line source) as well as to a single vehicle (point source). All traffic can be assumed concentrated on a single Sch.matic of Elevated Highway lane whose position is that of the single-lane equivalent as described in "Effect of Road Width and Observation Distance." The effective wavelength of traffic noise is about 2 to Observer 3 ft (i.e., the numerical attenuation of the dBA traffic noise lies close to the attenuation provided at a sound frequency /1 of about 500 Hz). Source / Automobile noise sources are located on or close to the road surface. The effective location of truck noise sources is somewhere between the road surface and the exhaust stack exit. b) Schematic of Depressed Highway The foregoing assumptions have not been validated experimentally but represent reasonable assumptions. On the basis of the design curves of Figure 8, Figures 9 and 10 have been developed. In these figures the attenuations for elevated and depressed highways, respectively, are shown as a function of certain parameters. These curves are Source V felt to represent adequately the acoustical performance of z -_.Observer the respective geometries as regards automobile traffic noise. They are limited to a 15-dBA attenuation due to refraction are arbitrarily reduced by 5 dB for trucks, due to theJigher location of truck noise source. c) Generalized Geometry of Acoustic Barrier

Shielding Adjustment Figure 7. Acoustic shielding geometrics. Three types of shielding are considered: (1) shielding by roadside barriers, (2) shielding by structures, and (3) shielding by plantings on the terrain between the roadway no 4v'uc.k re4iov c0 r b,r'rcr's and the observation position. see p5O This adjustment, as in the elevated-depressed case, is also Shielding by Barriers limited to —15 dBA, for the reasons mentioned previously. If the barrier does not shield the entire roadway element The attenuating influence of a solid, acoustically opaque under consideration, its effectiveness is reduced. A method roadside barrier has at, its origin the same physical princi- of evaluating the finite barrier adjustment is presented in the ples that were discussed with regard to the shielding influ- Design Guide. ence of elevated and depressed configurations. Thus, the design curve of Figure 8 is applicable and the same assump- Shielding by Structures tions concerning the source that are made in the section "Vertical Adjustment" are valid. The presence of buildings or structures on the terrain be- The resulting design plot is shown in Figure 11. In tween roadway and observer can have a significant shielding developing this plot it is assumed that the barrier is long effect. Sound penetration studies (14) indicate that this enough to effectively hide the total length of noise-producing shielding is effective for the first two or three rows of houses roadway. The degradation of performance caused by cur- and remains constant thereafter. Although no precise mea- tailing the length of a barrier depends on: surements are available in this area, a typical value of The potential performance of the barrier as set by its 3 to 5 dB per row of houses can be used (33). This attenua- height, noise source, and location relative to the observer. tion should not exceed a maximum of 10 dB and should be The total angle subtended at the observer by the applied only in cases where no direct line-of-sight exists unshielded portion of the highway. between observer and source. 16

-50 III 1111111111 11111111

° —30iii ____ C 1111111111 iuuoi 4. C 0 E 1111111 11111111 IIlii!HhiiiIIIII UIHi!jiPaIiiI1iiIDesign Curve —10 11111

0 jjlflIiiliIIIII 11111111 11111111 0 2 a/A Figure 8. Attenuation by acoustic shielding.

EQUIVALENT LANE OBSERVER

10 I 1111111 I 1111111 I__II _I 1111111 IAIIIllI__I__II

__I__IUlIIIINii!!!II

-20 IIUIHI I I. 4.0 6.0 8 - —

H2 / D5 Figure 9. Adjustment for elevated roadway. 17

EQUIVALENT OBSERVER LANE I Z DE

10 __•__huh __I 1111111__I__I _I 1111111 I1IHhhI__I__Iohm, I_IRIIUINii!!!IU -ST.- 1111111 • •iuuir a - a (D - Dc) Figure 10. Adjustment for depressed roadway.

EQUIVALENT OBSERVER LANE [nH

I DEDB 10 I •IIIIN I_1111111 I_I

0 0 _I_Ilh_I IluuhhI_I C I

4 -1 0 MENEM11111 _• IIIMU_I_ii IL_ -,n I 1111111 I IIIIIIFi- I - DB) Figure 11. Adjustment for roadside barriers.

Shielding by Landscaping Surface Adjustment In general, planting either at the roadside or the terrain The influence of road surface on traffic noise is discussed between the roadway and the observer position has little at some length by Galloway et al. (3). Based on this work influence on the propagation of traffic noise (3). Bushes, the adjustments of Table 2 have been developed to account trees, and similar foliage can attenuate sound only if the for deviations from "normal" surface conditions. These growth is dense enough and the depth of the foliage is great, adjustments are applicable to both automobiles and trucks. as some experimental measurements (11, 12, 13) indicate. A single line of trees or a depth of trees of less than Interrupted Traffic Flows Adjustment 50 to 100 ft will provide little actual attenuation; rather, the When traffic flow is interrupted, as by a STOP sign or signal, visual isolation may reduce a person's awareness of the noise it must be anticipated that the noise characteristics of that to a greater extent. traffic flow will be somewhat different from the same traffic A design value of 5-dB noise reduction for every 100 ft flow operating under a freely flowing condition. Unfortu- of planting depth may be used if these trees are at least nately at this time there is no clearly identifiable method of 15 ft tall and sufficiently dense so that no visual path be- modeling this type of traffic flow, and interrupted flows have tween observer and roadway exists. This attenuation should received sparse treatment in the literature. A modeling tech- not exceed 10 dB at a maximum. nique that might be suggested is a derivative of the technique used for predicting the noise from freely flowing traffic. In the freely flowing model, the sound power is related TABLE 2 to mechanical power expended by the vehicle at constant CLASSIFICATION OF ROAD SURFACE speed in overcoming rolling friction and aerodynamic drag. AS IT RELATES TO SURFACE INFLUENCE The same logic might suggest that the noise output of a ON VEHICLE NOISE vehicle at variable (stop-and-start) speed could be related ADJUST- to the mechanical power expended in this mode of opera- SURFACE MENT tion. The vehicle power in such operation is primarily TYPE DESCRIPTION (dB) expended on changing the vehicle speed, so a number of Smooth Very smooth, seal-coated parameters related to speed irregularity suggest themselves. asphalt pavement —5 Among these are the variance of the velocity, o, the Normal Moderately rough asphalt and variance of the acceleration, o- (or the standard deviation, concrete surface 0 Rough Rough asphalt pavement with a, which interestingly and confusingly enough is known to large voids ½ in. or larger the traffic flow theorists as "acceleration noise"), and in diameter, grooved concrete +5 weighted sums or mixed measures such as a a2 V(t). All of

_- Cross Traffic Volume Small Compared Main Highway

— — — — — — — — — — — — — — — — — — — — — — — — — — — /

------— — — — — — — — — — — — — — — — —

5Oft 5Oft i i 2 1.5miles (No Traffic Exits) 'I

Figure 12. Site of measurement study for interrupted flow effects. 19

these measures can be derived experimentally from a simple TABLE 3 velocity record taken with the "floating-car" technique. LEVEL ADJUSTMENT FOR INTERRUPTED FLOW To develop a better quantitative feel for the influence of flow interruption upon traffic noise, a series of measure- ADJUSTMENT (dB) VEHICLE ments was made on a section of roadway that permitted TYPE measurement of identical traffic flows under interrupted and L59 L10 non-interrupted conditions, respectively. Figure 12 shows Auto 0 +2 a plan of the roadway situation, and the two measurement Truck .0 + locations. Two microphone locations are shown: Position 1 is 50 ft from the center of the near lane, close to a signalized intersection. The intersecting roadway carries only a small volume of vehicles (relative to the main highway); microphone Position 2 is also 50 ft from the center of the near following considerations to specifying maximum desirable lane but located about 1.5 miles farther along the main traffic noise levels: highway. The length of highway between the intersection and the second microphone location is free from traffic The relation of highway noise to the ambient. exits and so the traffic volume and composition measured Task interference as associated with speech, sleep, at Position 2 is identical to that measured at Position 1. learning, and other on-going activities. Only the operating mode and speed of the vehicles are General annoyance (i.e., subjective satisfaction or different. dissatisfaction with the environment). The results of these studies are shown in Figures 13 and In selecting these approaches it is assumed that allowable 14, representing different measurement days. The data traffic noise levels will lie below those levels that are di- shown are the statistical time distributions, plotted on prob- rectly physiologically harmful (i.e., levels causing hearing ability paper, obtained from 20- to 30-min magnetic tape loss or extreme startle reaction, for example). recordings of the traffic. The recordings were not made The selection of noise criteria involves three separate simultaneously but within 45 min of each other. The solid elements: (1) the choice of the physical measure or rating curve represents the data obtained at microphone Posi- scale for the noise, (2) the choice of a procedure for tion 2 under the free-flow traffic condition. The dashed evaluating the effect of the noise, and (3) the selection. of line represents the data obtained at the signalized inter- numerical values to achieve the desired environment. Gallo- section Position 2. way et al. (3) examined the first element, choice of scale, On both measurement days the volume flows were close in detail. The results of that investigation led to the recom- to 4,000 vph. Speeds were estimated at close to 50 mph. mendation that traffic noise be described in terms of A- On the first measurement dam (Test 1) the percentage of weighted sound pressure level expressed in dBA. In this heavy trucks was counted at about 2%. A truck count was section, the second two elements, procedure and quantitative not obtained on the second measurement day (Test 2). values for criteria, are discussed. Both tests show the expected result that stop-and-start operating conditions increase the slope of the statistical time Relation To Existing Ambient distribution of traffic noise. Further, it is noted that the Highway noise is considered as an intrusion with respect to mean (50%) noise level is not significantly changed; thus, the ambient levels that existed or would exist in the absence the mean noise level for interrupted flow can be computed of the highway and its associated traffic. on the basis of the vehicle operating speed that would It has often been common practice to require that any prevail if the cause of flow interruption was removed. new noise intruding on an environment be controlled only Taking account of these data and considering the likely to an extent compatible with the existing ambient. When additional impact of interrupted flow conditions on 100% the new sound is broadband in nature, as in the case of truck traffic, the corrections for interrupted flow are given traffic noise, with no time or frequency characteristics that in Table 3. The quantitative corrections for interrupted flow clearly identify it, the intruding levels can be higher relative are felt to be sufficiently small as to reduce the immediate to the ambient than if the new source of sound contains need for a model that represents the interrupted flow situa- pure-tone components or has intermittent time properties. tion in detail. Thus, Table 3 is used in the Design Guide. The clear consequence of a philosophy that permits each new noise intrusion to equal the existing noise environment CRITERIA FOR HIGHWAY NOISE is, of course, an upward creep of the environmental noise levels in 3-dB steps. Although such a situation is not par- In the development of highway noise criteria, the research- ticularly desirable, the process may not elicit too much ers have considered values and methodology previously response from the affected communities—until, of course, derived on several different, although not unrelated prem- such time as the environment becomes unacceptable from ises, and have arrived at criteria that they believe should the viewpoint of task interference or general annoyance. be used as design goals in the highway planning process. The purpose here is to examine the extent to which in- The principal consideration underlying all such criteria is trusion of traffic noise above the ambient is permissible some measure of subjective (human) response to noise. without incurring an unreasonable penalty in terms of sub- These responses, in turn, are reflected in one or more of the jective response. Fundamental to this approach is an under-

98 98

95 95 '4 \\ '4 — — — — — Interrupted Flow (1) ------Interrupted Flow (1) Free Flow (2) all Free Flow (2) '4 80 80

-o 70

0.5 0.5

0.2 0.2 Al Al 55 60 65 70 75 80 85 90 95 55 60 65 70 75 80 85 90 95 Noise Level In dBA Noise Level in dBA Figure 13. Results of interrupted flow study—Test 1. Figure 14. Results of interrupted flow study—Test 2. 21

standing of the correlation between objective measures of some value judgment must be made concerning the maxi- the noise and probable subjective reactions. To this end, mum permissible noise level. several general principles deriving from past experience in One concept of highway noise criteria based on this community noise studies are cited. intrusion-versus-ambient approach states simply that the It is generally changes in the environment rather than mean traffic noise levels (dBA) should not exceed the range absolute levels that precipitate public reaction. This notion, of mean ambient levels (measured or estimated) character- of course, does not extend to very high levels, but is prob- istic of the type of area of concern. Some typical ambient ably valid over a large range of situations that presently levels are shown in Figure 15. occur for traffic noise. The assumption is that ambient Intermittent excesses due, for instance, to passing trucks levels that have existed for some time have come to be should not exceed the range of ambient levels by more than accepted as satisfactory or are considered beyond the con- 10 dBA. It is noted that extraordinary events such as very trol of public reaction. No doubt, symbiotic relationships close truck passages or low aircraft flyovers may produce develop with time whereby people acclimatize to their en- levels that exceed ambient levels by 25 to 35 dBA; although vironment, provided exposure is not too severe. There is people may be acclimatized to such events, if they occur evidence to indicate that just the opposite may obtain when frequently, individual or public complaints may be precipi- levels are too high. At any rate, it is desirable that altera- tated. Thus, the 10-dBA excursion allowed for infrequent tion of the subjective acoustic environment be avoided or events by the foregoing criterion is conservative. Excesses minimized. of less than 5 dBA above the ambient range probably will Next, it might be postulated that the magnitude of change cause no significant complaints, whereas intermittent peaks will depend on the degree of intrusion that the new source of 5 to 10 dBA are only marginally acceptable. Ten- to bears to the ambient, and this of course will depend on the 15-dBA excesses may signal a potentially serious problem, time-varying characteristics of both the new source and the and peaks greater than 15 dBA or so would probably initiate existing ambient. strong individual or concerted public action. Traffic noise is most meaningfully described as a "statisti- Several comments can be made concerning the foregoing cal time distribution" of levels. Three useful values of the scheme for highway noise criteria. First, it is premised on distribution are the levels that exceed for 10%, 50%, and the assumption that existing ambient levels are, not likely to 90% of the time. the ambient itself commonly derives change in the future. Second, the resulting criteria for from traffic sources and thus is also characterized by a dis- traffic noise will prove acceptable only to the extent that the tribution with time; so, it is necessary in assessing the degree present environment is judged acceptable; further attenua- of intrusiveness of traffic noise to superimpose two random tion of traffic noise, however, is wasted effort as no benefit variables, each described by its own statistical properties. will accrue to the area. The criteria developed in the fore- Typically, noise due to such random processes as traffic flow going manner assure that relatively quiet areas remain quiet has a nearly Gaussian time distribution, and the probability while noisy areas require less stringent noise control mea- density representation is symmetrical about the mean value. sures. Some upward creeping of the over-all environment Knowing, for instance, the 10% and 90% levels of both the is allowed by this procedure. Finally, it should be noted existing ambient and the intruding highway noise, one can that application of these criteria is not everywhere possible. mathematically ascertain the percentage of the time for In very quiet areas, it is simply not possible to avoid alter- ing the environment, and in these cases it is necessary to which the intrusion will be above or below the ambient, set realistic design limits on the noise levels consistent with assuming well-behaved statistical properties of both signals. annoyance- and task-related requirements. In many cases, Experience has shown that large variations in acceptable introduction of a highway will significantly raise the am- noise levels result from different individual subjective eval- bient levels, and no reasonable amount of noise control will uations of highways. Indeed, evidence of this phenomenon prevent the change from being measurable, noticeable, and suggests that it is meaningless to design for other than the even objectionable. Whenever the amenity afforded by the average response with some margin of safety. In general, margin between the existing ambient and the maximum people of higher socio-economic status demonstrate greater permissible level is compromised, public reaction probably sensitivity to highway noise, and property owners are more will ensue. conscious of the deleterious effects of noise on property Sawley and Gordon (14) have developed guidelines for values than are apartment dwellers. The adjustment for the predicting community response to a steady intrusive noise subjective "meaning" of intruding highway noise is difficult when the intruding level is related to the statistical distribu- to estimate and is beyond the scope of desired generality. tion of the ambient. These results are given in Table 4. A significant part of community response to noise is When the intrusion is characterized by a statistical time- determined by conditions that prevail inside of dwellings level distribution, one can establish analytically the sub- and other occupied buildings. Some account must be taken jective exposure on the basis of percentage time audibility. of the inside levels as well as those outdoors. Knowing the The acoustic interpretation of the mathematics is rather noise reduction properties of typical building constructions, complicated except in simple cases. one can determine what indoor noise levels result from Given the mean levels (X0, Y0) and standard deviations outdoor sources and deduce the amount of intrusion. (o, o) of two normally distributed random variables, Inevitably, the situation will arise in which the ambient X (highway noise) and Y (ambient), the following ques- noise level is exceeded by the intrusive contribution and tions might be asked: For what percentage of the time will PIN

80 "DOWNTOWN" COMMERCL&L AREAS WITH HEAVY TRAFFIC

INDUSTRIAL AREAS 70 -o C COMMERCIAL AREAS LIGHT TRAFFIC

-60

URBAN RESIDENTIAL EM AREA (DAYTIME)

QUIET SUBURBAN AREA (NIGHTTIME)

30 Figure 15. Typical continuous background noise levels.

the signal, X, exceed the ambient, Y? For what relative 1 P(Z>Q)=—J e 212du (28) positions of the two distributions will X exceed Y by a. dBA for a given percentage of the time? To answer the first question, one needs to know the in which probability that Z = X - Y is greater than zero. This is u= (Z—Z)/o, obtained by evaluating =xo — Yo (29)

Scra= Vo.2+o.2 and P(Z> 0) is tabulated for various values of the upper TABLE 4 limit of integration. EXPECTED COMMUNITY RESPONSE ON BASIS Typically, the standard deviations, a-,, and are nearly OF COMPARISON OF INTRUDING NOISE LEVEL equal. Further, experience has shown that a realistic value TO STATISTICAL DISTRIBUTION OF AMBIENT of o (and o- ,) is 5 dBA; thus, o = 7 dBA. NOISE LEVEL Eq. 28 dictates then that for X to be greater than Y for 10% of the time (i.e., the noise is audible for 10% of the LEVEL OF INTRUDING NOISE (IL) time) the condition on the respective mean levels is X0 = RELATIVE TO THE AMBIENT NOISE EXPECTED COMMUNITY — ( 1.28)(1.41)o= Y0 —9 dBA LEVEL (AL) RESPONSE Y0 - 1.288cr = Y0 Similarly: for 50% audibility, X0 = Y0; for 90% audi- IL AL No observed reaction <50% bility, X0 = Y0 + 9 dBA; and for 99% audibility, X0 = 50% AL < IL < 10% AL From no observed reaction to sporadic complaints Y0 + 16 dBA. 10% AL 1% AL Widespread complaints and X0 = Y0 + 1 dBA; and similarly for 50%, 90%, and 99% possible community action of the time, X0 = Y0 + 10 dBA, X0 = Y0 + 19 dBA, and

a From Sawley and Gordon (14). X5 = Y0 + 26 dBA, respectively. 23

Now, if the guidelines of Table 4 are interpreted in terms TABLE 5 of the implied audibility, one finds that for the (assumed) EXPECTED COMMUNITY RESPONSE ON BASIS equal statistical properties of the traffic noise and ambient OF COMPARISON OF MEAN LEVELS OF INTRUDING distributions, with the common standard deviation equal to NOISE AND AMBIENT NOISE 5 dBA, anticipated community response can be related following the Composite Noise Rating (CNR) approach EXPECTED COMMUNITY to the mean levels as given in Table 5. NOISE LEVEL RESPONSE It is interesting to note that the mean level of an intruding X, < Y0 No observed reaction source with a statistical time distribution may be higher than Y. Y. + 16 dB Widespread complaints and is an increase of approximately 2.5 dBA. possible community action It should be observed, also, that the development pro- From Sawley and Gordon duced previously is premised on normal (Gaussian) distri- (14). butions of both the ambient and the highway noise. This approximation is clearly inapplicable to low-density traffic flow. Modification of the foregoing analysis is possible, however, when the actual distribution can be expressed analytically. (This adaptation has not been produced as It seems futile to attempt to eliminate all complaints, be- yet.) cause there will always be a few in the population who are unusually sensitive to noise. Therefore, a Composite Noise Translating the information of Table 5 into highway noise Rating of C criteria, it is apparent that it is desirable to keep the mean can be chosen to describe the design environment from which one would expect, on the average, only traffic noise level below the mean of the ambient. Because a few occasional complaints. this is not generally possible, it is necessary that mean To find the noise level rank. Y, of the trffiç noi&@ alono, intrusive levels be. less than 9 dB above the mean ambient the predicted octave band traffic levels are overlaid on a level to preclude more than sporadic complaints. series of curves termed "level rank" curves. These curves To what extent accommodation of subjective response approximate a set of equal loudness curves separated by occurs with time is uncertain at present and this factor 5-dB intervals. The level rank into which the highest octave cannot, and probably should not, be included in the cri- band sound pressure level (SPL) protruded is selected as terion. It seems likely that when levels are high enough to the primary descriptor of the magnitude of noise in the occasion more than sporadic complaints, the acclimatization CNR calculation procedure. process is reversed (i.e., objections increase with longer The rationale for categorizing the noise levels in 5-dB exposure). increments was based primarily on experience (16) Composite Noise Rating Techniques indicating that In 1953, studies (15, 16) were undertaken to review the the range of variation normally encountered in the reaction of residents of a community to a given noise is suffi- case histories of community noise problems in complaint ciently wide that a change of noise level of less than 5 situations and to derive a method of predicting average dB would not produce a significant change in the general community response to noise. This resulted in the Com- pattern of reaction to the noise. posite Noise Rating (CNR) system developed by Rosen- The authors (16) believed that an attempt to specify a blith, Stevens, and Bolt. noise environment of a community to a precision greater Primary importance was placed on the over-all level and than 5 dB was unrealistic. spectrum shape of the intruding noise. However, adjust- Background noise level in the community was expected ments were included for the level and spectral characteris- to be a significant element in the determination of com- tics of the ambient noise in comparison with the intruding munity response. Thus, typical ambient levels (in octave noise. Other adjustments were included for time, duration, bands) can be overlaid on a family of curves, similar to the and frequency of noise source operation, seasonal effects, "level rank" curves, to obtain a correction factor, K1. Al- previous community exposure, and the temporal characteris- ternatively, the value of K1 can be selected from Table 6, tics of each event. Thus, adjustments were introduced due which is based on the various types of areas. Note that a to both the physical properties of the intruding noise and correction of one numeric unit corresponds to a change of attributes of the noise receiver, the community. one letter rank in Composite Noise Rating. Figure 16 shows the interpretation of Composite Noise A second correction factor, K2, derives from considera- Ratings in terms of community response (16). Note that tions of the time of day of noise source operation, per- a range of response is indicated for a given CNR rating. centage of an 8-hr period that source operates, and seasonal From Figure 16 one might select the desired probable effects that relate to open and closed windows. Because it response of the community and work backwards to the is assumed that the source (i.e., the highway) operates dur- limiting intrusive levels consistent with this response. The ing both nighttime and day, for 100% of an 8-hr period worst-case design might limit noise to the extent that com- (for automobiles), and during summer as well as winter, plaints are directed to noise source operators and officials. correction factor K2 is taken to be zero to cover the worst

RESPONSE Vigorous Community Action

Range of Expected Response from Communities Threats of Community Action

Wid.spread Complaints

Sporadic Average Expected Response Complaints

No Observed Reaction A B c D E F G H Composite Noise Rating Figure 16. Expected range of responses from communities exposed to noise of increasing severity (from Ref. 16).

combination of situations. At particular times, this value of correction factors defined previously. It is desired to solve K2 may be incorrect, but clearly one must design for the Eq. 30 for Y, given that X = C, K1 is variable, K2 = K3 = worst circumstances. 0, and K. = —1. Thus, accounts for the spectral content Correction factor K3 Y=C—K1 +1=D—K1 (31) and the temporal nature of the intruding noise. Because highway noise is broadband in spectrum and generally of Knowing the constraint on Y from Eq. 31, one can estab- a non-impulsive character, K3 = 0. lish the maximum permissible octave band level for auto- In the prediction of community response, the final result mobile traffic, and, for fixed spectrum shape, subsequently takes the form determine the A-level associated with the design condition on Y. For a generalized auto spectrum, Eq. 31 can be (30) X=Y+K1 +K2 +K3 +K4 rewritten as in which X is the Composite Noise Rating; Y is the noise L2 =49-6K1 dBA (32) level rank of the intrusion; and K1 through K4 are the in which K1 is defined previously; and La is the A-weighted spectrum level. Considering noise due to truck traffic, the arguments concerning correction factors are generally the same as for TABLE 6 automobile traffic. If it is assumed that truck traffic is COMPOSITE NOISE RATING CORRECTION NUMBERS audible for approximately 20% of the time, K2 = —1 and TO ACCOUNT FOR DAYTIME AMBIENT NOISE the expression for the design noise level rank is LEVELS IN TYPICAL NEIGHBORHOOD Y=C—K1 + 1 — 0 + 1=E—K1 (33) CORREC- TION or, in terms of A-weighted levels, NEIGHBORHOOD NO. La 565K1 dBA (34) Very quiet suburban +1 Suburban 0 Several comments should be made concerning the Com- Residential urban —1 posite Noise Rating method of Rosenblith, Stevens, and Urban near some industry —2 Bolt. It is interesting to note that, in the case of automobile —3 Area of heavy industry traffic noise, the critical portion of the spectrum is the part associated with speech interference. This aspect of sub- From Rosenblith et al. (16). 25

jective response to noise is discussed later. The strength of have been used to determine satisfaction of employees with this methodology is that is takes cognizance of how people the environments in which they work. The net result of (as communities) actually do respond to their acoustic this study was that people tended to rate their surroundings environment, at least on the basis of their complaint. It on the ability to converse either in face-to-face communi- does not include details of noise reduction by special ex- cation or using a telephone. Noise criteria (NC) and terior constructions and the variations in the attenuation alternate noise criteria (ANC) curves were subsequently properties of buildings. In applying criteria deriving from derived. More recently in Great Britain and in Europe Composite Noise Ratings, it is probably necessary to con- calculated descriptors such as the traffic noise index (TNI) sider truck and automobile traffic flows separately and then (19), the energy equivalent level (Q) (20), and the noise make a judgment of acceptability on the more critical pollution level (LNP) (21) have been developed in an situation. attempt to correlate objective measures of the sound field The CNR scheme has survived over the years with and subjective responses to social surveys regarding noise various modifications. Although it has not received a interference with residential life patterns. systematic validation examination, it has been used in many Consider first speech communication as a basis for estab- practical noise control cases. lishing maximum allowable noise levels due to highway Among such applications, the CNR concepts have been traffic. The underlying problem is the detection of a signal applied to prediction of community reaction to aircraft (speech) above some noise background (traffic noise). noise (17). In this application, noise levels are expressed It must be decided what minimum speech intelligibility, as in terms of the perceived noise level, expressed in PNdB. given by the articulation index, is acceptable for any por- The CNR value is calculated by adding to the perceived tion of the time. Alternatively, one may establish the frac- noise level of the source, adjustments for: tion of the time for which it is tolerable to allow speech The number of events per day. communication in some design talker-listener configuration to deteriorate beyond a given point. The resulting con- The time of day at which events occur (day versus night). straints on highway noise can be calculated in a straightforward manner. Average duration of the events, in the case of ground runup noise. Because traffic noise is nearly always described in terms of a statistical time distribution, speech intelligibility must There is no correction for ambient levels, because com- also be considered to vary statistically with time. Rather munity survey studies had shown that background noise than specifying a single value of acceptable or desirable levels, per se, had little influence on community response intelligibility, it is the percentage intelligibility exceeded to the typically high noise level intrusions produced by jet for some part of the time that must be controlled. Note aircraft. that the acceptability of X% intelligibility for Y% of the time is not fully understood. In addition, the influence of Speech Interference the characteristic time scale of variation as between the In developing highway noise criteria on the basis of task 10% and 90% levels is not sufficiently grasped to be in- interference, one is interested in the ways that noise pro- cluded in the present scheme. The basic approach here is hibits or inhibits the performance of various functions. to assure very good intelligibility for some minimum per- These activities include speech communication, sleep, and centage of the time and to permit deterioration beyond television and radio use. Task interference seems a valid marginal intelligibility for some smaller part of the time. and important premise for criteria for the following A review of the literature relating speech intelligibility to reasons: the objective quantity called articulation index, shows that an articulation index of approximately 0.40 represents the For a given type of area, one can define the activity point at which communication is effectively stopped with- or activities characteristic of the land use, and in this regard out a change in voice level or a change of separation dis- the maximum noise levels consistent with utility can be tance. This articulation index is associated with word ascertained. intelligibility of the order of 60% and sentence intelligi- Task-related evaluation of the acoustic environment bility less than 90% (22). On the other hand, an articula- is given to more objective measurement than are subjective tion index of 0.60 implies word intelligibility in excess of evaluations of annoyance. Particularly in the area of 83% and sentence intelligibility greater than 95%. The speech interference, a great deal of research has been done researchers propose that criteria should be premised on an that enables the identification of objective levels associated with functional performance capabilities. articulation index of 0.60 prevailing for at least 50% of the time and, further, that the articulation index be less than Design criteria in the past have consistently been 0.40 for no more than 10% of the time.* given in terms of task interference measures such as speech interference levels (SIL), and articulation index (Al) From the method of calculating articulation index de- values. tailed by Kryter (23) for preferred frequency octave bands, the following is derived: During the past 25 years many investigations of speech communication have been performed, and the present-day * Robinson (21) has suggested that".., it seems sufficient for general planning to adopt the simple rule: analysis is well developed. Indirect tests, such as Beranek's for normal conversation conditions, aim at [an articulation index of] questionnaire survey of office-type environments 0.4 (18), for difficult conditions, aim at [an articulation index of] 0.6...... 26

(dBA) for various talker-listener configurations and voice Al = 2.4639 - 0.0333(La G) (35) levels are given in Tables 7 and 8. where the generalized automobile spectrum shape has been From the derived model of traffic noise, described in the assumed to represent the traffic noise and is accounted for previous sections, it is seen that for high-density traffic in the constant 2.4639. Truck traffic will be considered flows and/or when the point of observation is sufficiently later. The term G includes effects of voice level and distant from the line of vehicles, the range between the speaker-listener distance. G = 0 for normal voice level at 10% and 50% levels is small enough that the 50% cri- 3-ft distance and increases 6 dB for each increment in terion is applicable. Nearer the roadway and at lower voice level as from normal voice to raised voice, raised density flows, the 10% criterion controls. To distinguish voice to very loud voice, and varies by 6 dB per doubling between low- and high-density flow, consider the idealized of talker-listener separation. The foregoing expression situation of uniformly spaced vehicles forming a single-lane gives the time-varying value of articulation index as a linear equivalent composed of a single type of vehicle. If the function of the instantaneous traffic noise level, La (dBA), configuration in which the 10% and 50% levels differ by and G. Rearranging Eq. 35 to solve for La, the maximum 6 dBA is selected as a transition point between the two flow allowable noise levels due to automobile traffic can be regimes, the condition on traffic density, p (vehicles/mile), obtained for design values of Al. and observation distance, D (ft), is (39) 2.4639—Al pD = 600 ft-veh/mile (36) La 0 .0333 +G This defines the crossover point between low-density flow for which the 10% criterion (Al> 0.40) should apply and = 0.60 corresponding to the 50% traffic Substituting Al high-density flow for which the 50% criterion (Al> 0.60) noise level, should be satisfied. La5o=56+dBA (37) Considering the situation in which the levels exceeded for 10% of the time or less are dominated by a single and, similarly, the 10% level is given by vehicle, it is found that the corresponding condition on La1062+GdBA (38) traffic density and observation distance is pD 1,650 ft-veh/ mile (40) Both La50 and Laio are abbreviated in the Design Guide to L50 and L10. Clearly, over the range of applicability of the low-density Clearly, when the difference between the 50% and 10% traffic model, the 10% and higher levels (10% to 0%) levels is less than 6 dBA, satisfaction of the 50% level are the result of the single nearest vehicle and the traffic criterion automatically implies compliance with the 10% noise might more easily be described in terms of the peak level specification; and, conversely, when the difference be- levels due to the individual vehicle passage. Subjectively, tween the 10% and 50% levels exceeds 6 dBA, satisfaction it is the peak levels that characterize low-density traffic of the 10% criterion is the sufficient condition. Using flow, and it seems fitting that criteria should be couched in Eqs. 37 and 38, maximum allowable traffic noise levels these terms.

asslng Vehicle

spacing

Figure 17. Distance at which noise from a passing vehicle is within y dBA of its peak value. 27

TABLE 7 TABLE 8 TRAFFIC NOISE LEVELS (CONTINUOUS SOURCE, TRAFFIC NOISE LEVELS (DISCRETE EVENT MODEL, AUTOS ONLY); A-LEVELS NOT TO BE EXCEEDED AUTOS ONLY); A-LEVELS NOT TO BE EXCEEDED BY L TO PROVIDE AN ARTICULATION INDEX BY L,10 TO PROVIDE AN ARTICULA lION INDEX OF 0.60 OF 0.40

VOICE LEVEL (dBA) VOICE LEVEL (dBA) VERY VERY DISTANCE (Fr) LOW NORMAL RAISED LOUD DISTANCE (FT) LOW NORMAL RAISED LOUD 1 60 66 72 78 1 66 72 78 2 54 84 60 66 72 2 60 66 72 78 3 50 56 62 68 3 56 62 68 74 4 48 54 60 66 4 54 60 5 66 72 46 52 58 64 5 52 58 64 6 44 70 50 56 62 6 50 56 62 68 12 38 44 50 56 12 44 50 56 62

Accordingly, the peak level due to a single passage can effects are included in predicting the actual peak levels at be related to the 10% level. Because the 10% level for the locations of interest. Eq. 44 might also be written in this low-density traffic flow is determined by the single terms of the permissible levels observed at some standard nearest vehicle, one first defines the distance, 2AD (Fig. distance as 100 ft. This is perhaps a fabrication, because 17), over which noise from the passing vehicle is within the situation in reality might be observation at 200 ft, ydBA of the peak value. From the traffic density p and with some of the noise-reducing constructions located observation distance D, one can select a value of A cor- between 100 and 200 ft from the highway. The resulting responding to a value of y representing the 10% noise level. equation, however, is The result (not surprisingly) is 4100, :!~ 22 + 10 log 6 x 10\ (41) (1+ 69(pD)2 )+G-2O log D (45) in which T (ft) is the assumed uniform vehicle spacing. Sleep Interference Recalling the derived expression for conversion from dBA to articulation index, observe that a 3-dBA change in Much of the previous work regarding traffic noise inter- La corresponds to a change of 0.1 in Al. If X is defined as ference with sleep has been concerned with social survey the articulation index-at the peak noise level, then the response and spontaneous complaints indicating the condi- articulation index can be expressed as tions under which people have difficulty falling asleep or are awakened from sleep. More recently, Thiessen and 6.96x 104 '\ Al,0 =X+ 1/3 lo(l + (42) Olson (24) have investigated the effects of noise on the (pD)2 , electroencephalograph of sleeping persons. The noise in which Al10 is the articulation index corresponding to the source is a recording of a truck passage. The duration of 10% noise level and the generalized automobile spectrum the recording is 29 see, with the peak occurring at approxi- has been used to describe the noise source. For Al10 to be mately the center of the time interval and having a level always greater than or equal to 0.40, about 35 dB above the level at the start and finish of the noise sample. The level is within 5 104\ dB of the peak for 6.96 x approximately 1.2 sec X ~ 0.40— 1/3 log (i + (43) (25). Using this stimulus, it was (pD)2 ) found that (26), "Some subjects may awaken more than Combining this expression with Eq. 7 gives 50% of the time at a peak noise level of the passing truck of 50 dBA while others practically never awaken, even at 6.96 x 104 75 dBA." This illustrates the broad range of subjective LD < 62 + lolog(1 + + G (44) sensitivities. Even (pD)2 at a disturbance level of 70 dBA, the ) most probable reaction (awakening) is obtained in only which defines the constraint on the peak level, L0, due to 30% of the cases. At levels of 40 to 45 dBA there is a a single vehicle such that the articulation index will be not 10% or greater chance that subjects will change level of less than 0.40 for more than 10% of the time. This, then, sleep or awaken. is the low-density traffic noise criterion. It was found in 1957 (27) that for a steady noise raised Note that nothing is said here regarding attenuation in 5-dB steps, at 3-min intervals, more than half the sub- other than hemispherical spreading assumed in the traffic jects were awakened when the level reached 45 dB. Also model. Equivalently, Eq. 44 could be rewritten in terms found was a wide range (35 dB) of noise levels that awaken of required noise reduction provided special attenuation individual subjects. 28

Clearly, although absolute numbers are becoming avail- interference have been offered. Beranek (29) suggests that able to statistically describe sleep interference, there are indoor levels not exceed 40 to 45 dBA for television and many questions that must be answered before criteria can radio listening. Note from Table 7 that this implies normal be developed on the basis of sleep considerations. voice communication at 12- to 15-ft separation. The Wilson Committee Report (30) on noise problems Other Criteria Developments in England suggested tentative criteria for levels not to be Particularly in Great Britain and in Europe (19, 20, 21), exceeded inside living rooms and bedrooms for more than several measures of noise exposure have been developed in 10% of the time in various types of areas. These values attempts to describe the aspects of noise that determine are given for day and night conditions as follows: subjective response. The principal technique has been to look for improved correlation between the physical mea- NOISE LEVEL (dBA) surements (time-level distributions) and subjective response AREA DAY NIGHT to social survey questions. Intuition suggests that much of the subjective evaluation Country 40 30 of one's acoustic environment depends on peak levels that Suburban (away from main traffic) 45 35 intrude above the ambient. This approach somewhat paral- Busy urban 50 35 lels that of Rosenblith, Stevens, and Bolt. A descriptor in present use, entitled traffic noise index (TNI) was pro- Where speech communication is a vital consideration, the posed by Griffiths and Langdon (19). Searching for a Wilson Committee recommended that maximum back- high degree of correlation between the 10% and 90% ground levels (inside) not exceed 55 dBA. This excludes measured levels and social survey response, Griffiths and factories and auditoria, which represent special situations. Langdon defined TN! as Other criteria derived on the basis of jury ratings of individual vehicles have been produced by Mills and = 4 (L,10 - L La90 - 30 (46) TN! aoo) + Robinson (31) who showed that the demarcation between Any convenient units may be used, such as dBA, PNdB, "acceptable" and "noisy" vehicles as judged by a panel of or over-all SPL. Note that the traffic noise index weights 57 listeners is 79.5 dBA for automobiles, 80.5 dBA for the intrusive element of the environment, as represented by diesel trucks, and 82.5 dBA for motorcycles. ambient described by the 10% level. The final constant is These results are believed to represent the point at which the quantity (Laio - La90), four times as much as the people will change their evaluation of a passing vehicle ambient described by the 10% level. The final constant is from satisfactory to unsatisfactory. Mills and Robinson included only as a scale adjustment to match their particu- further suggest that, to avoid virtually all unsatisfactory lar set of interview data. The time interval over which the judgments, the foregoing levels should be reduced by 10% and 90% levels are to be taken is 24 hr. With regard 12 dBA. to developing criteria, the only significant effort has been In the U.S., Pearsons and Horonjeff (32) asked subjects by Langdon and Scholes (28) who looked for a correlation to rate the noise of both motor-vehicle drivebys and air- between TN! values and over-all acceptability of the en- craft flyovers on several different category scales. Little vironment. They have plotted TN! versus percentile and difference was found between category judgment scales for absolute dissatisfaction scores. Selecting the lower 95% the various types of motor vehicles. On a "noisiness" confidence level at 50% dissatisfaction, they find that for category scale, the demarcation between "moderate" and an urban residential situation a TN! value of 74 dBA gives "noisy" category ratings for out-of-door field judgments 1 chance in 40 that a subject may rate his environment as was about 89 PNdB (or about 76 dBA). marginally unsatisfactory or worse. Because traffic is gen- Robinson (21) has attempted to rationalize a number of erally the major source of observed disturbance in urban the foregoing considerations as well as other studies of areas, it might be construed that TN! = 74 dBA is a reaction to noise in his concept of "noise pollution level," reasonable highway noise criterion. symbolized by LPN. His expression contains two terms, Several facts concerning TN! should be noted. First, one relating to the energy averaged mean noise level, Lea, assigning a value of TN! does not select an absolute level and the other a measure of the variation of the instanta- but, rather, fixes the range between 10% and 90% levels neous levels around the mean. This expression is empiri- as either the 10% or 90% level is allowed to vary. In the cally derived as unusual case of vanishing dynamic range, the maximum LPN = Lea + 2.56a (47) permissible steady level is given by the value of TN!. Second, note that typical noise-reducing configurations do in which ,- is the standard deviation of the instantaneous not necessarily reduce the 10% and 90% levels equally. level. For a Gaussian distribution of noise, this equation To use the convention of TN! = 74 dBA as a design cri- may be written as terion, one must assign an allowable maximum level to LPN =Lao +d+ (d2/60) (48) either the 10% or 90% level. Presumably this fixed value would be based on considerations of desirable mean or in which d is the interdecible level range. peak levels such as developed previously in regard to When the noise levels are expressed in dBA, Robinson speech interference. obtains from several social surveys an LPN value of about Other criteria referenced directly or indirectly to task 80 dBA at the 50% dissatisfaction level. 29

Comparison of Methods TABLE 9 Comparing the results of the several approaches to highway DESIGN GOAL NOISE LEVELS AS PER METHOD noise criteria just discussed, one finds that over much of OF ROSENBLITH, STEVENS, AND BOLT the dynamic range of interest the results derived on the different bases are similar. This can be shown by some NORMAL NORMAL simple examples. VOICE VOICE TALKER- TALKER- From Eq. 32 deriving from the method of Rosenblith, AUTO LISTENER TRUCK LISTENER Stevens, and Bolt, design goal levels for nearly steady noise LEVELS DISTANCE LEVELS DISTANCE due to auto traffic are given in Table 9. Considering the TYPE OF AREA (dBA) (FT) (dBA) (FT) 10% noise levels to be dominated by truck traffic, the Very quiet suburb allowable levels given by Eq. 34 are also given in Table 9. (rural) 43 13 51 11 For comparison, the corresponding talker-listener distances Suburb 49 7 56 6 for normal voice communication outdoors are indicated Residential urban area 55 3.5 61 3.4 from Tables 7 and 8. The distances are seen to be similar Urban area near for both truck and auto traffic, and are not unlike the some industry 61 2.2 66 2 values that might be estimated for the general types of Heavy industry areas. area 67 1.1 71 1.1 For guidelines used previously by the researchers for highway noise control consulting work, based on the spectrum shape of NC curves, suggested daytime noise criteria for automobile traffic are given by the values in Table 10. noise index (TN!), specification of a design value of TN! Because truck traffic (and motorcycles and sport cars) are does not determine the actual criterion levels, but rather more usually responsible for intermittent peaks, they are limits the dynamic range as expressed by the 10% and not included in the development of Table 10. A quick 90% levels. Investigating the range of 10% levels sug- comparison of the numbers in Tables 9 and 10 indicates gested by Speech criteria (38 to 78 dBA), one finds that that the latter criteria based solely on ambient considera- limiting TN! to 74 dBA allows the 10% to 90% range to tions are comparable to those derived for speech and the vary between 20 and 31/2 dBA. At lower levels, the spread ambient/intrusion method of Rosenblith et al. is allowed to be greater than at higher levels. The inherent As observed in the previous discussion of the traffic shortcoming of the TN! procedure is that insufficient data

TABLE 10 OUTDOOR NOISE LEVELS (AMBIENT) USED AS DESIGN GOAL CRITERIA IN RESIDENTIAL AREAS

DAYTIME OUTDOOR EVENING OUTDOOR NIGHTTIME OUTDOOR TRAFFIC NOISE TRAFFIC NOISE TRAFFIC NOISE LEVEL LEVEL LEVEL (dBA) IF THROUGH: (dBA) IF THROUGH: (dBA) IF THROUGH: DWELLING OPEN CLOSED OPEN CLOSED OPEN CLOSED AND AREA WINDOWS WINDOWS WINDOWS WINDOWS WINDOWS WINDOWS Single-occupancy dwellings in low-density population area (rural or urban) 47-52 55-60 42-47 50-55 39-44 47-52 Single-occupancy dwellings in medium-density population area 52-57 60-65 47-52 55-60 44-49 52-57 Multiple-occupancy dwellings in low-density population area 52-57 60-65 47-52 55-60 44-49 52-57 Multiple-occupancy dwellings in medium-density population area 55-60 63-68 50-55 58-63 47-52 55-60 Single-occupancy dwellings, hotels, luxury-type apartments, or hospitals in high- density population area 57-62 65-70 52-57 60-65 49-54 57-62 Multiple-occupancy dwellings or non-luxury apartments in high-density population area 60-65 68-73 55-60 63-68 52-57 60-65 30

maximum limits beyond which property is no longer of the are available to establish an absolute limit or set of limits for either the 10% or 90% levels involved in calculating design utility. On the other hand, there are compelling arguments for trying to preserve any amenity by constrain- TNI. Arguments not cited here have been given that subjective ing the degree of excursion of highway noise levels above the existing ambient. For these reasons, it is believed that evaluation of the environment is based on fewer considerations than suggested by the number of rating systems in highway noise criteria should develop along parallel paths, one deriving from speech interference considerations and current use. For instance, it is conceivable that people judge general annoyance as if they were trying to converse the other relating to the ambient. The criteria that are in some typical talker-listener arrangement. The attention- advocated are as follows: distracting mechanisms with regard to sleep may be much Highway noise should not cause the articulation index the same as for reading, conversation, or TV/radio use. at the position of interest to be less than 0.60 for more than It is difficult to separate general annoyance as manifest by 50% of the time in the most critical (yet typical) speech social survey or complaints from specific task interference. communication configuration. Further, the articulation Similarly, intrusion/ ambient criteria probably are related index in the foregoing situation should not be less than to interference of the acoustic environment with perform- 0.40 for more than 10% of the time. Resulting criterion ance of certain functions, be they as passive as sleep. levels (Tables 7 and 8) derived for average voice and assumed ideal conditions should be reduced by 6 dBA to Selection of Criteria to Be Used in Highway Design. account for variations in voice levels, female voices, and In the foregoing discussion of possible highway noise cri- uncertainties in the design talker-listener configuration. teria, the researchers do not attempt to detail all the many This reduced level is to be considered a design goal, with procedures developed in the past, but rather to survey the 6-dBA higher value a design limit. representative fundamental considerations underlying the Corrections to the articulation index development should methodology. Clearly, the choices are multitudinous, and be included as necessary to account for building transmis- in any given situation certain conditions must weigh more sion loss, reverberant room effects, and changes in noise heavily than others. Because the highway designer cannot spectrum shape due to frequency-dependent attenuation. perform extensive analyses of all the configurations and Table 11 gives some estimated speech communication community situations along the route of a proposed high- requirements typical of various types of areas. way, the selection of design goals must be made as simplc Over the high-density traffiô flow tegime, pD> 600 and as straightforward as possible. This entails a value ft-veh/ mile, mean traffic noise levels should exceed the judgment of the emphasis to be placed on various aspects mean ambient level by no more than 9 dBA where the of the acoustic environment. In the following, the re- standard deviations of both highway noise and the ambient searchers develop the criteria that they believe should be dBA, and both time-level distribu- used by the highway designer/planner in assessing the have been taken to be 5 are assumed normal. In the situation that the stan- impact of the proposed highway on the adjacent areas and tions dard deviations can be measured or estimated more accu- in considering desirable or required noise reduction. It has been noted that task-related criteria are best rately than the assumed 5-dBA value above, the more rig- La5o 5~ Y0 + 1.28o, adapted to preservation of land use and, in this sense, set orous relation between mean levels is

TABLE 11 RECOMMENDED DESIGN CRITERIA

L. (dBA) L10 (dBA) OBSERVER DAY NIGHT DAY NIGHT CATEGORY STRUCTURE Insides 45 40 51 46 i Residences 51 Residences Outside 50 45 56 2 40 46 46 3 Schools Inside 40 - 61 - 4 Schools Outside 55 Inside 35 35 41 41 5 Churches 41 Hospitals, Inside 40 35 46 6 45 56 51 7 convalescent homes Outside 50 8 Offices: Inside 50 50 56 56 Stenographic 46 Private Inside 40 40 46 9 Theaters: Inside 40 . 40 46 46 Movies 36 Legitimate Inside 30 30 36 45 56 51 10 Hotels, motels Inside 50

Either inside or outside design criteria can be used, depending on the utility being evaluated 31

in which a-- is defined by Eq. 34 and Y0 is the mean ambient of the general public change throughout the typical 24-hr level. The value of L050 determined here should be con- cycle. For instance, in a given location, the tasks with sidered a design goal. which noise may interfere vary from sleep in the early morning to speech outdoors in the early evening to TV use In the design process, it is believed that criteria in terms later at night. Although it would be desirable to define of speech interference as well as related to the ambient levels of subjective sensitivity as a continuous function of should be evaluated and the highway design should be pre- time, this is not possible. A more practical approach is to dicated on the lower of the two resulting design goals. divide the 24-hr day into two intervals defined as daytime (0600 to 2000 hr), and nighttime (2000 to 0600 hr). In Time Considerations the development of the highway design, the usual approach Considerations of the time of day that highway noise occurs is to establish a critical situation that combines high noise have not been explicitly discussed. Time effects no doubt levels (steady or peaks) and high subjective sensitivity. enter the selection of criteria as the subjective sensitivities These details are incorporated in the Design Guide format.

CHAPTER THREE

APPLICATIONS

To provide for rapid application of this research, two aids given as Appendix A. The second is an "Illustrative Re- have been developed for the highway designer. The first cording of Traffic Noise," the text for which is given in is a "Design Guide for Traffic Noise Prediction"; this is Appendix B.

CHAPTER FOUR

CONCLUSIONS AND SUGGESTIONS FOR FUTURE RESEARCH

In the course of this research program various aspects of point noise level estimates are desirable. The large amount traffic noise have been investigated. Central to the studies of data handling necessary to develop contours suggests that was the development of a design tool by which highway traffic noise calculations be "computerized." Two distinct engineers can introduce traffic noise as a parameter in road- levels of complexity for computer calculations are sug- way design and route planning. Inevitably, however, as in gested to meet the widely varying needs of the highway any application-oriented research, more questions are raised designer. than can be answered with the available resources. The One immediate approach is a computer program in which following paragraphs suggest some specific topics for further the Design Guide noise prediction methods can be digital- research. ized. The design data given in the tables and shown in the graphs would be stored in the computer and the computer HIGHWAY TRAFFIC NOISE CALCULATIONS would be used as a "look-up" device and as a "bookkeeper," Actual application of the Design Guide in several express- in adding and tabulating the various corrections for indi- way design studies has contributed insight into the prob- vidual roadway elements and in calculating the final lems faced by designers for highways transversing estab- estimated noise level. lished urban areas where both noise levels and land use are The basic computer programing for such an approach is critical. In such cases, noise contours rather than single- straightforward. However, it is believed that the program 32 would be particularly useful if it was carefully programed cover and vegetation during different seasons of the year for a variety of either "time sharing" or "remote terminal" may add a further seasonal effect that influences the computers. Special emphasis should be given to developing performance of barriers. an "easy-to-use" program that could be used by engineers It is considered important to know the probable extent having access to a simple teletype input terminal. of such variables on barrier performance and the variation Experience in estimating the noise environment for ex- in performance that is likely to be encountered in practice. pressways and expressway interchanges for urban areas, It is believed that study of the performance of practical particularly those having irregular terrain, suggests that barrier constructions and the study of long-term variability application of the design guide steps often requires serious in traffic noise levels at distances out to 1,000 ft from an simplifications of highway design and terrain features. expressway can be obtained by a "demonstration" project. Because of the great complexity of the calculations in Such a project would involve the construction of several such a situation, accompanied by need for relatively ac- types of full-size barriers placed near an existing highway, curate estimation of noise levels at many ground locations, with acoustic measurements made at various distances from a much more complex computer program development is the expressway. The acoustic measurements should be made envisioned. Such an approach would use a large-capacity, under a sampling basis over an extended period of time— high-speed computer facility and would be used primarily a number of months, for example. It is believed that such for detailed design studies of critical sections of expressway a demonstration project could be conducted in conjunction routes. with the experimental programs of one or more state high- Rather than the approach adopted in the Design Guide, way departments. the whole topographical situation for the proposed design would be introduced into the computer storage. This could ATTENUATION DUE TO STRUCTURES AND be done by graphical tracing of the detailed topographical INTERVENING BUILDINGS maps developed for the expressway design. Ultimate out- One of the shortcomings of the Design Guide is lack of put of the program would be the calculation of the noise reliable experimental data in the area of shielding by struc- levels for ground positions on a mesh or grid system. From tures. The available data do not describe adequately the the output of the grid values, noise contours could be type and density of buildings where the measurements were readily drawn by hand. performed. A measurement program of attenuations where Simulation of the traffic noise sources could be based on the type (commercial, residential, rnulti-stuiy) and density distribution of sources along the actual roads or routes of of structures are the variables is suggested to define this interest. Time distribution statistics might also be incor- adjustment more precisely. porated, using some of the basic approaches developed in the traffic simulation program described by Galloway et al. (3). TIRE.ROADWAY NOISE A major source of traffic noise produced by both auto- DEMONSTRATION PROJECT—BARRIERS AND mobiles and trucks, and particularly noticeable for current PROPAGATION OF TRAFFIC NOISE passenger cars at high speeds, is noise due to tire-roadway In the Design Guide, noise level estimates for traffic noise interaction. The source mechanisms are complex, and and adjustments in noise levels for barriers or intervening many characteristics of the tire, the roadway, and the objects are given that are believed to be relatively con- vehicle suspension are important in producing the noise. servative and represent long-term averages. In the field, the, At present, specific source mechanisms are not well-defined, basic performance of a barrier may be modified by many nor are many quantitative measurements available. Yet, parameters of the barrier design and of the environment in detailed understanding and control of this noise source is which the barrier is placed. For example, the terrain, the essential for any long-term progress in sizable reductions ground cover, and variations in the height of effective of the noise produced by motor vehicles. sources of noise for automobiles and trucks may modify The technical complexities of the tire noise problem and the performance of barriers. Although some of these fac- both immediate and long-term needs for quantitative in- tors can be usefully studied by laboratory scale-model tests formation suggest major program effort in at least two and by mathematical analysis, the influence of other factors complimentary approaches: cannot be accurately duplicated in the laboratory, nor can they be easily handled by analysis. Acquisition of accurate data on the noise produced At distances of more than 100 ft or so from a barrier, the by tire-roadway interactions for current tire-roadway com- attenuation produced by the barrier may be subject to varia- binations under controlled test conditions. Detailed and tion on an hour-to-hour and day-to-day basis, even under accurate quantitative measurements are needed for both constant traffic flow conditions. The sources for these varia- immediate applications in tire and roadway design, in tions arrive from the basic inhomogeneity of the atmosphere estimating traffic noise, and in providing input for assessing near the ground. This inhomogeneity includes turbulence, the importance of different noise-source mechanisms. which causes scattering, as well as temperature and wind Basic study of the physics of the noise-source and gradients, which cause bending of the sound waves. The noise-transmission mechanisms involved. Such a program variation in ground impedance due to changes in ground would involve theoretical, analytical, and laboratory studies, 33

with the aim of developing mathematical formulations amount of energy (i.e., 3 dB per doubling), but it is difficult defining tire-roadway noise generation and radiation. to demonstrate this in psychophysical tests. The complexities of the noise problem, both from mea- A noise situation that continually reoccurs in traffic surement and analytical aspects, suggest that those efforts situations is that where a number of discrete noise events intrude on a relatively high-state background noise level just described should be a sizable long-term effort, en- compassing programs extending over at least a several-year (e.g., the presence of trucks on a busy freeway). This is period. a situation that is poorly understood from the standpoint of either speech intelligibility or annoyance assessment. Other related problems exist that suggest the need for EFFECTS OF TIME-VARYING NOISE ON SPEECH, research for extrapolation of current knowledge of the SLEEP, AND ANNOYANCE effects of steady-state noise to non-steady-state cases of There is considerable knowledge about the effects of steady- practical importance. Such areas of research would include state noise on speech intelligibility and the relative annoy- judgment tests to determine the effects of: ance of individual noise-producing events. However, the Variation in amplitude versus number of events. effects of time-varying noise and the multiplicity of noise Variations in the fluctuation of noise levels from long- events have not been thoroughly investigated. For example, term averages. accurate estimates of the intelligibility of speech in a given The combinations of steady-state and discrete noise steady noise environment can be made. Similar predictions events of varying dynamic range and' frequency of for slowly varying, non-steady-state noise at various points occurrence. in time can be obtained; however, the problem of an individual's over-all assessment of the environment if different Additional areas of research involving speech interfer- amounts of speech interference or interruption are present ence should include tests to determine: over long periods of time has not been investigated. The effect of the amount of interruption on a person's A person's assessment of the noise environment when the assessment of his environment. number of noise events is varied is also unknown. It has The effect of the rate of interruptions, and whether been assumed that the noisiness or annoyance varies as the the interruptions are random or periodic.

REFERENCES

Urban Noise-Strategy for an Improved Environment. FEHER, R. 0., Proc. Am. Nat. Noise Abatement Symp. Org. for Econ. Coop. and Development (Oct. 1969). P.98 (1951). DONLEY, R., "Community Noise Regulation." Sound BRINTON, J. H., JR., Effects of Highway Landscape and Vibration, 3, (2) (Feb. 1959). Development on Nearby Property. Franklin Inst. Re- GALLOWAY, W. J., CLARK, W. E., and KERRICK, J. S., search Lab. (1969). "Urban Highway Noise: Measurement, Simulation, WIENER, F. M., and KEAST, D. H., "Experimental and Mixed Reactions." NCHRP Report 78 (1969). Study of the Propagation of Sound Over Ground." J. Acoust. Soc. Am., 31, 724-733 (1959). ROBINSON, D. W., COPELAND, W. C., and RENNIE, HARRIS, C. M. (ed), Handbook of Noise. A. J., "Motor Vehicle Noise Measurements." The McGraw- Hill (1957). Engineer, 211, (5488), 493-497 (Mar. 1961). SAWLEY, R. J., and GORDON, C. G., "A Comprehen- JOHNSON, D. R., and SAUNDERS, E. G., "The Evalua- sive Survey of the Noise in Communities Around tion of Noise from Freely Flowing Road Traffic." Boeing Field, Seattle." Report 1709, Bolt Beranek and J. Sound and Vibration, 7, (2), 287-309 (1968). Newman, Inc. (Jan. 1969). "Objective Limits for Motor Vehicle Noise." Report ROSENBLITH, W. A., STEVENS, K. N., and the Staff of 824, Bolt Beranek and Newman, Inc. (Dec. 1962). Bolt Beranek and Newman, Inc., "Handbook of STEPHENSON, R. J., and VULCAN, G. H., "Traffic Acoustic Noise Control. Vol. II: Noise & Man." Noise." J. Sound and Vibration, 7, (2), 247-262 WADC Tech. Report 52-204, (June 1953). (1968). STEVENS, K. N., ROSENBLITH, W. A., and BOLT, R. H., MAEKAWA, Z. E., "Noise Reduction by Screens." "A Community's Reaction to'-Noise: Can It Be Fore- Applied Acoustics, 1, 157-173 (1968). cast?" Noise Control, 1,63 (Jan. 1955). REDFEARN, S. W., Philosophical Magazine, 7, (30), Land Use Relating to Aircraft Noise. Prepared by 223 (1940). Bolt Beranek and Newman for the FAA (Oct. 1964), 34

including Appendix A (May 1965). Also published as Private communication from G. J. Thiessen. "Land Use Planning with Respect to Aircraft Noise." Press release by G. J. Thiessen. AFM 86-5, TM 5-365, NAVDOCKS p-98, Dept. of Research on Urban Traffic Noise: Progress of Re- OECD, •Directorate for Defense. search in Various Countries. BERANEK, L. L., "Revised Criteria for Noise in Build- Scientific Affairs, Internat. Coop. in Urban Research, ings." Noise Control, 3, 19-27 (Jan. 1957). Paris (24 May 1968). GRIFFITHS, I. D., and LANGDON, F. J., "Subjective LANGDON, F. J., and SCHOLES, W. E., "The Traffic Response to Road Traffic Noise." J. Sound and Vibra- Noise Index: A Method of Controlling Noise Nui- tion, 8, (1), 16-32 (1968). sance." Building Research Station Current Paper RATHE, E. J., and MUHEIM, J., "Evaluation Methods 38/68 (1968). for Total Noise Exposure." J. Sound and Vibration, BERANEK, L. L., Acoustics. McGraw-Hill (1954). 7, (1), 96-115 (1968). Noise-Final Report of the Committee on the Problem ROBINSON, D. W., "An Outline Guide to Criteria for of Noise. The Wilson Committee, HMSO, London the Limitation of Urban Noise." NPL Aero Report (1963). Ac39 (Mar. 1969). MJLLS, C. H. G., and ROBINSON, D. W., "The Sub- KRYTER, K. D., "Validation of the Articulation Index." jective Rating of Motor Vehicle Noise." The Engineer J. Acoust. Soc. Am., 34, (11), 1698-1702 (1962). (30 June 1961). KRYTER, K. D., "Methods for the Calculation and Use PEARSONS, K. S., and HORONJEFF, R. D., "Category of the Articulation Index." J. Acoust. Soc. Am., 34, Scaling Judgment Tests on Motor Vehicle and Aircraft (11), 1689-1697 (1962). Noise." FAA Report DS-67-8 (July 1967). THIESSEN, G. J., and OLSON, N., "Community Noise- Noise Environment of Urban and Suburban Areas. Surf ace Transportation." Sound and Vibration, 2, (4), Prepared by Bolt Beranek and Newman, Inc., for the 10-16 (Apr. 1968). U.S. Dept. of Urban Development (Jan. 1967). 35

APPENDIX A

DESIGN GUIDE FOR TRAFFIC NOISE PREDICTION

How will the introduction of a new highway influence the of the calculation procedure is discussed. Finally, some noise environment? How acceptable will this new environ- comments are presented concerning the response of people ment be to people living or working in the vicinity of the to noise environments. highway? What methods might be pursued to remove or Section Three presents an overview of the methodology reduce any adverse influence caused by the highway noise? used. The parameters considered in a traffic situation are The purpose of this Design Guide is to provide the highway defined and the procedure involved in calculating an esti- designer with tools necessary to answer these questions. mated noise level from a proposed highway discussed. Two The province of noise and the physics of acoustics lies methods of predicting noise levels are introduced: (I) somewhat outside the range of the highway engineer's complete method, and (2) short method. normal training and experience. For this reason, rather Section Four gives detailed step-by-step instructions for than provide an acoustical textbook—which might confuse the "complete method" calculations. These instructions are rather than help the engineer—the researchers have at- paralleled by complete work sheets, figures, and tables tempted to develop a design "cookbook." The intention through which the user progresses to obtain the estimated throughout has been to provide a tool that the designer with outside noise level for , a particular roadway. These figures no experience in acoustics can use, and use quickly and and tables are given in Exhibits A and B. effectively. Section Five gives stepby-step instructions for the "short The format used is as follows: method" calculations. Section One gives a glossary of definitions and symbols. Section Six shows the procedure through which the esti- Section Two introduces the reader to the basic concepts mated outside noise levels are interpreted in terms of design on which the noise prediction method used in this Design criteria. The criteria presented are based on both environ- Guide is based. An understanding of these concepts is mental utility, such as speech and sleep requirements, and important if the user is to make adequate decisions in using environmental conservation. This is done for a variety of the guide. The section, first of all, introduces the basic observer situations for both outside and inside conditions. parameters of environmental noise, because these parame- In addition, the section discusses the expected impact on ters are the ones that the Design Guide must set out to the community when the estimated levels exceed the design calculate. Then the analytical model that forms the heart criteria.

SECTION ONE—GLOSSARY OF TERMINOLOGY

This section contains a glossary of the terminology used poses, this range is usually taken to include frequencies throughout the Design Guide. This glossary is divided in between 20 Hz and 10,000 Hz. three main groups: DECIBEL (dB) = a logarithmic "unit" that indicates the Acoustical Terminology: Contains the definition of ratio between two powers. A ratio of 10 in power cor- all terms that are acoustical in nature. responds to a difference of 10 decibels. Roadway Terminology: Contains the definitions as- dBA* = the sound pressure levels in decibels measured with sociated with the roadway design and evaluation. Where a frequency weighting network corresponding to the "A- possible, these definitions are consistent with the ones used scale" on a standard sound level meter. The A-scale tends in the "Highway Capacity Manual," HRB Special Report 87 to suppress lower frequencies (e.g., below 1,000 Hz). (1965). FREQUENCY = the frequency of a sine wave of sound is the Definition of Symbols: Contains the definition of all number of times it repeats itself in each second. The unit symbols used in the Design Guide. of frequency is called the hertz, abbreviated as Hz, or the cycle per second. ACOUSTICAL TERMINOLOGY * In interpreting traffic noise levels in dBA, one may note that a change AMBIENT NOISE LEVEL = the noise level existing in an area of 10 dBA corresponds to a subjective judgment of the halving or doubling of the noisiness of the sound. In other words, a sound judged to be twice before the proposed roadway. This quantity is measured as noisy as another sound would have a sound pressure level rating ap- in dBA and expressed as L10 or L50 ambient noise levels. proximately 10 dBA greater than the first sound. A sound 20 dBA greater than the first sound would generally be rated as four times as noisy as the AUDIBLE SPECTRUM = the frequency range normally as- first sound. On the other hand, a difference of 1 or 2 dBA between sounds, sociated with human hearing. For noise control pur- although detectable if heard within a short time interval, would not be judged as a very significant difference by most observers. 36

FREQUENCY BAND = an interval of the frequency spectrum NORMAL ROADWAY = when roadway element surface is defined between an upper and lower "cut-off" frequency. moderately rough asphalt or concrete surface. The band may be described in terms of these two fre- PAVEMENT = that part of the roadway having a constructed quencies, or, preferably, by the width of the band and by surface for the facilitation of vehicular movement. the geometric mean frequency of the upper and lower PERCENTAGE GRADIENT = change in roadway elevation per cut-off frequencies (e.g., "an octave band centered at 100 ft of roadway. 500 Hz"). ROADWAY ELEMENT = a section of roadway with constant Hz = the abbreviation for frequency in hertz. characteristics of geometry and vehicular operating LEVEL = an adjective used to indicate that the quantity conditions. referred to is in the logarithmic notation of decibels, with FINITE ROADWAY ELEMENT = when roadway element starts a standardized reference quantity used as the denomi- and finishes within the 8 DN limits of the roadway, where nator in the decibel ratio expression. DN is the observer-near lane distance (see Fig. B-i). REFERENCE MEDIAN LEVEL = the L50 level measured 100 ft INFINITE ROADWAY ELEMENT = when roadway element from the single-lane-equivalent roadway element with the length is larger than 8 DN, where DN is the observer-near element assumed infinitely long and located at grade on lane distance (see Fig. B-i). a flat, level terrain. SEMI-INFINITE ROADWAY ELEMENT = when roadway ele- SINGLE-LANE EQUIVALENT OF A ROADWAY = that single-lane ment extends across 4 DN in one direction but termi- representation of the roadway which, to the observer, is nates within the 8-DN roadway length, where DN is the acoustically similar to the real roadway. observer-near lane distance (see Fig. B-i). SOUND LEVEL = a corruption of the term "sound pressure ROADWAY SURFACE = determines the roadway surface char- level." acteristics (see smooth, normal, or rough roadway). L10 = sound level that is exceeded 10% of the time. ROUGH ROADWAY = when roadway element is a rough asphaltic pavement with voids ½ in. or larger in L50 = sound level that is exceeded 50% of the time. diameter, or grooved concrete. SOUND PRESSURE LEVEL (SPL) = the root-mean-square sound pressure, p, related in decibels to a reference SHOULDER = that portion of the roadway between the outer pressure. The value reads directly from a sound level edge of the through traffic pavement or the curb or the point of intersection of the slope lines at the outer edge meter. of the roadway and the fill, or median slope. Sound pressure level = 10 log P2 /ref 2 in which = 0.0002 microbar. SMOOTH ROADWAY = when roadway element surface is very Pr,f smooth, seal-coated asphaltic pavement. SPEED = the rate of movement of vehicular traffic, ex- ROADWAY TERMINOLOGY pressed in miles per hour. AT-GRADE ROADWAY = when roadway element is level with TRAFFIC LANE = a strip of roadway intended to. accommo- the immediate surrounding terrain. date a single line of moving vehicles. AUTOMOBILES = passenger vehicles other than motorcycles, TRUCKS = trucks of greater than 10,000-lb gross vehicle trucks of less than 10,000-lb gross vehicle weight, buses weight, buses having a capacity for more than 15 having capacity for 15 or less passengers. passengers. AVERAGE ANNUAL DAILY TRAFFIC (AADT) = the total VOLUME = the number of vehicles that pass over a given yearly volume divided by the number of days in the section of a lane or roadway during a time period of i hr year. or more. Volume can be expressed in terms of daily traffic or annual traffic, as well as on an hourly basis. AVERAGE ROADWAY SPEED = the weighted average of the design speeds within a roadway section. DEFINITION OF SYMBOLS BARRIER = infinite or finite walls located near the roadway-oadway and parallel to it. Such walls must be solid and not A = general parameter. undçrcut. B = general parameter. CAPACITY = the maximum number of vehicles that has a C = general parameter. reasonable expectation of passing over a given section of D = distance parameter, measured between observer a lane during a given time period under prevailing traffic and nearest point to center line of roadway, in conditions. feet. DEPRESSED ROADWAY = when roadway element is depressed DB = distance parameter measured between observer below the immediate surrounding terrain. position and barrier, in feet (see Fig. A-7). ELEVATED ROADWAY = when roadway element is elevated Do = distance parameter, measured between observer above the immediate terrain. and cut of roadway, in feet (see Fig. A-6). INTERRUPTED FLOW = a condition in which a vehicle tra- = distance parameter, measured between observer versing a section of a lane or a roadway is required to and equivalent lane of roadway, in feet (see stop by a cause outside of the traffic stream, such as signs Fig. B-i). or signals at an intersection or a junction. Stoppage of DN = distance parameter, measured between observer vehicles by causes internal to the traffic stream does not and center of near lane of roadway, in feet (see constitute interrupted flow. Fig. B-i). 37

Ds = distance parameter, measured between observer SA = speed parameter, measured as above, for auto- and shoulder of roadway, in feet (see Fig. A-6). mobiles. dB = (see Acoustical Terminology.) ST = speed parameter, measured as above, for trucks. dBA = (see Acoustical Terminology.) V = vehicle volume parameter, in vehicles per hour; H = height parameter, in feet. this represents the total volume of automobiles L = length parameter, measured along a roadway ele- and trucks mixed. ment (finite), in feet. VA = vehicle volume parameter, in vehicles per hour, L10 = (see Acoustical Terminology.) for automobiles only. L50 = (see Acoustical Terminology.) VT = vehicle volume parameter, in vehicles per hour, N = number of traffic lanes on roadway. for trucks only. P = width parameter, measured from outside to out- = angle parameter, measured as included angle beside lane on roadway, in feet. tween observer and barrier, in degrees. RB = distance parameter measured between equivalent O = angle parameter, measured as included angle be- lane and barrier, in feet (see Fig. A-7). tween observer and roadway element (finite) and S = speed parameter, measured as the average speed complementary angle (semi-infinite roadway), in of vehicular flow, in miles per hour. degrees.

SECTION TWO—BASIC CONCEPTS

In the following paragraphs some of the basic concepts and responding short-term noise fluctuations are also randomly findings of the studies that have led to the development of occurring. this Design Guide are discussed. It is felt that an apprecia- Environmental noise level variations on the macroscopic tion of these will help the reader to use the guide more time scale can be handled by analyzing the traffic flow situa- effectively and to bring good judgment to bear where tion at different time intervals during the 24-hr day. Such judgment is necessary. a procedure is convenient because the requirements that a person places on his environment also change from one time PARAMETERS OF ENVIRONMENTAL NOISE interval to another. The three dimensions of environmental noise that are of Short-term variations are most sensibly accounted for particular concern in determining subjective response are: statistically. The "statistical time distribution" identifies I. The intensity or level of the sound. each level within the environmental range with the percentage of time that that level, over the short term, is The frequency spectrum of the sound. exceeded. The 50% The time-varying character of the sound. level (or median level) is that level that is exceeded for 50% of the time. The 10% level is The first two of these dimensions are adequately handled that level that is exceeded for 10% of the time. These two in the case of traffic noise by measuring or calculating the descriptors of the "statistical time distribution," symbolized sound in terms of the "A-weighted" sound level. The by L50 and L10, respectively, play an important role in this A-scale reading of a standard sound level meter provides a Design Guide. single number measure of the noise stimulus that "weights" the frequency spectrum of the signal in accordance with PREDICTION OF TRAFFIC NOISE subjective sensitivity to sounds of different frequency. The A-scale reading therefore (in dBA units, meaning decibels, The maximum noise emitted by an automobile as it passes A-scale) provides a measure of the level and spectrum of an observer increases, approximately, with the third power the stimulus that correlates well with subjective response to of road speed. The noise output of a diesel truck, on the the stimulus. other hand, shows little dependence on road speed. A truck, The third dimension reflects the fact that environmental of course, is also very much noisier than an automobile. It noise is rarely constant; it is changing from second to is assumed in this Design Guide that the bulk of highway second, from minute to minute, and from hour to hour. traffic can be classified into one or another of these two Road traffic is by far the most common source of environ- vehicle classifications. Appropriate definitions are given in mental noise, and environmental noise levels tend to follow the glossary (Section One). closely traffic activity. Consider now a single-lane pavement that is straight and On the macroscopic time scale, therefOre, environmental infinitely long, and that lies at grade with respect to a flat, noise is highest during the day, and especially during the level terrain. The members of each vehicle classificatiOn morning and afternoon traffic peaks. Levels reach their are considered uniformly distributed along the lane, and lowest values during the night when local traffic activity all each vehicle classification is categorized by volume flow but ceases and arterial activity becomes small. (vehicles/hour) and average (group) speed (miles/hour). On the microscopic time scale, environmental noise fol- Analysis of this rather idealized system shows, when the lows the moment-to-moment details of traffic patterns. Such density of vehicles per unit length is sufficiently high, that patterns are effectively randOm in time, and thus the cor- the sideline noise for the automobile population increases 38 linearly with the volume flow and increases with the third in individual differences in thresholds of annoyance, ha- power of average speed. Under the same conditions, on bituation to noise over differing past experiences with noise, the other hand, the noise of the truck population increases the semantic content conveyed by specific sounds, and the linearly with the volume flow but decreases linearly with meaning of the source of noise itself. increase in average speed. This apparent paradox is ex- In terms of task interference with speech or sleep, plained by the fact that the noise of an array of trucks is quantitive evaluations of criteria, although difficult, are dependent only on the density (in vehicles per mile) of the more easily obtained. For example, many data exist con- vehicles. For constant volume flow the density is inversely cerning the effects of a steady masking noise on the in- proportional to speed. telligibility of speech in different environments or speech A further finding of the analysis is that sections of road- conditions. Data also exist on what noise levels are con- way that subtend equal angles at a fixed observer location sidered desirable in different speech environments (e.g., contribute equally to the observer's noise environment. continuous noise levels that should not be exceeded if Furthermore, the contribution is directly and linearly pro- adequate telephone use is to be expected, or what levels portional to the angle subtended. Thus, the noise contribu- of noise permit acceptable TV listening for most people). tion of any finite element of roadway can be derived from The effect on speech interference of noises that are inter- the infinite roadway model. mittently higher than the average to which the listener is Further, non-ideal attributes of real roadway systems can exposed is not yet well understood. be accommodated by adjustments to the finite roadway The effect of noise on sleep interference is more difficult model, as follows: to assess than the effect on speech interference. Study of 1. Any realistic number of lanes, with or without median sleep interference is difficult because of the different physio- separator, can be collectively grouped as an "equivalent" logical states of sleep and the fact that sleep interference single lane, provided the lanes lie in the same horizontal can exist without a person being consciously awakened. plane and are not obstructed acoustically from each other. Recent experiments do provide guidelines, however, in con- The appropriate adjustment is determined by the relation sidering sleep interference effects in the selection of design of the near and far lanes to the observer. criteria for traffic noise. 2 Vertical translation of the roadway to an elevated or Moving from laboratory data to the results of social depressed position, with respect to the terrain, can also be surveys of traffic noise adds some insight in the develop- accommodated if an adjustment is made to the predicted ment of criteria'. These surveys help determine percentages noise levels to account for the shielding effect imposed by of people having different responses to various noise the vertical displacement. The extent of shielding depends sources. When the results of the surveys are examined on the extent to which the roadway configuration blocks against physical descriptions of the noise environment, in- the sightline between the observer and the equivalent single formation can be developed on at least the significant physi- lane representative of the roadway. cal measures of noise that contribute to the variance in the A real roadway system, therefore, having the real at- general response of a community to noise. It is worth tributes of curves, gradient changes, cross-section changes, observing that physical descriptions alone generally account flow changes, etc., can be synthesized as a number of finite for less than half the components of variance in response (or semi-infinite) discrete roadway elements. The noise of to noise, with the other non-physical factors mentioned each element can be derived from the infinite roadway earlier often dominating. model with adjustments to account for each of these real Certain general factors may be deduced from the present attribtues, as is shown in the following sections. body of laboratory and social survey studies: Interference with speech or TV listening is the pre- REACTION TO ENVIRONMENTAL NOISE dominant complaint against traffic noise. The effects of noise on people fall into three general Interference with sleep is often cited as a complaint. Both a measure of the time-average noise level and categories: measures of the magnitude and rate of occurrences of peak Subjective effects of annoyance, nuisance, dissatis- noise levels are important in describing people's response faction. to traffic noise. Interference with activities such as speech, sleep, learning. On the basis of the foregoing considerations, suggested Physiological effects such as startle, hearing loss. design criteria for traffic noise have been derived (Table B-5). These criteria specify maximum noise levels that The noise levels associated with traffic noise are, in almost would be considered by the average individual to be accept- every case, of concern only in the first two categories. able with respect to speech, radio and TV interference, sleep Unfortunately, there is no satisfactory objective measure of the subjective effects of noise. In laboratory evaluations it interference, and annoyance. is possible to quantify the comparative subjective reactions Numerous situations exist where people are now living between different sounds. However, no experiments yet with traffic noise levels that are in excess of those specified provide an adequate absolute measure for subjective re- in Table B-5. This is not to say that these noisy environ- action. This result stems primarily from the wide variation ments are entirely satisfactory; rather, people will either 39 accept an unsatisfactory noise environment, move away people will find acceptable, even though lower levels might from it, or attempt to bring legal action to reduce the noise. often be desired. The researchers believe that exceeding The design criteria presented are, on the other hand, higher these criteria by more than 5 dB will provide environments in some instances than are considered desirable by some in which the majority of people would express a major public authorities. They are presented as realistic goals that dissatisfaction.

SECTION THREE—THE METHODOLOGY OF TRAFFIC NOISE PREDICTION

In the previous section some of the basic concepts involved Traffic parameters describe the "idealized" traffic in defining and analyzing the highway noise environment situation on the road element. Vehicle volume defines total are discussed. The intention in this section is to describe number of vehicles that pass a point on the road element in general terms the methodology used in the Design Guide. during 1 hr. Vehicle mix describes the proportion of heavy The general traffic situation is composed of an infinity of trucks in the population. As discussed in Section Two, variables; different cars driving at different speeds through truck noise has different characteristics from automobile continuously changing highway configuration and sur- noise and must be treated separately. Average speed de- rounding terrain. Obviously, to make the problem prac- scribes the average speed of vehicles on the road element. ticable, certain assumptions and simplifications must be Note that this parameter is especially important for auto- made. This is done through a model of the traffic situation mobiles because the noise emitted increases with the third that defines the most important parameters involved and power of speed, whereas it remains constant for trucks. thus permits the prediction of the true situation with a Roadway characteristics are described by five parame- certain degree of accuracy. The flow diagram that illus- ters that define the geometry of the road element with trates the methodology is shown in Figure 1 and is discussed respect to the immediate surroundings. Pavement width in the following. defines the distance across the roadway; this distance does not include outside emergency lanes. Vertical configura- DEFINITION OF PARAMETERS tion describes the roadway elevation or depression with Consider a highway transversing a populated area. The respect to the surrounding terrain. Flow characteristics simplest case would be to assume a perfectly flat and relate to flow interruption imposed by roadway design. straight road of constant cross section, carrying a constant Gradient defines the percentage of gradient of the roadway. vehicle volume. Thus, observers at different positions along Surface characteristic describes the "roughness" of the the highway, each at a distance of 400 ft, would be sub- pavement. jected to the same, unchanging noise level. In this simple Observer characteristics describe the location of the case, the highway can be defined as a constant infinite noise roadway element with respect to the observer and take source. On the other hand, if the road geometry is not account of the attenuating influence of the intervening constant with respect to the observer (elevated or de- terrain. Observer distance defines the perpendicular dis- pressed sections, four lanes changing to two lanes, curves, tance between the observer and the roadway element. etc.) the infinite noise source model no longer is true and Element size is defined by the angle subtended by the elements of constant the geometry must be discretized into element at the observer. Shielding describes all acoustical In reality, because a practical model is be- characteristics. shielding present between observer and road element. Ob- ing dealt with, these constant characteristics are allowed to server relative height describes the observer vertical position vary within certain practical limits; for example, a con- with respect to the roadway. tinuous change in elevation of 5 ft over a 1,000-ft span can be neglected. For the purposes of this discussion, a road element is PROCEDURE defined as that section of the road whose geometrical con- The foregoing three groups of parameters must be known figuration (straight, level, constant cross section, etc.) with each roadway element to predict the noise level for a respect to the observer and whose traffic density and speed for observer location. Consider again the example given over the element length can be considered constant. Fig- single earlier of a single roadway element, infinitely long and of ure 1 indicates that for a general case, N different road constant characteristics located at grade on a flat, level element are possible. terrain. Furthermore, locate the observer 100 ft from the Each road element identified can be described by a series road, with no shielding present. This, for practical con- of parameters that must be known or measured. These siderations is considered the "worst case" or the noisiest parameters can be grouped under three headings: condition (obviously, points closer to the road will be sub- Traffic parameters. jected to higher noise levels, but such points are seldom Roadway characteristics. of interest). The noise level at 100 ft is called the reference Observer characteristics. noise level. This reference noise level is measured as a The step-by-step method of obtaining these parameters is median level, called L50 (the 50% level is that level that treated in detail in Section Four. Their role in the method- is exceeded for 50% of the time). Under the assumptions ology of the Design Guide may be summarized as follows: of the model, reference noise levels can be obtained by 40

I Road Elements I

Traffic Parameters Roadway Characteristics Observer Characteristics

Pavement Width Vehicle Volume •VerHcal Configuration Observer Distance Vehicle Mix S Flow Characteristics Element Size Average Sp - •Gradient Shielding Surface Observer Relative Height

Adjustments Reference Noise Level at 100 ft

[I i stance Predicted Table _o Level-L50 Noisej Elev/Depr Predicted Noise Level H at Observer - L50 Short Method Evaluation Element Criteria > Criteria < Short Method Short Predicted Noise Level Method Gradient at Observer - L10 I! Acceptable Noise I Shielding I Environment No Further Criteria J Analysis Req'd [SHORT METHOD ONLY

Complete Method Possible Problem Evaluation Complete Analysis R e q u i r e d Figure 1. Flow diagram of traffic noise methodology.

knowing the traffic parameters only and will yield two a height, H. The observer, standing below the level of the numbers, one for automobiles and one for trucks, measured roadway, is wholly or partially shielded from the vehicular in dBA. noise sources depending on the extent of elevation. Some Deviations from this simple model will introduce pa- attenuation of the radiated traffic noise is, therefore, im- rameters from the roadway characteristics and observer posed. A further adjustment will occur if the observer characteristics groups and will result in adjustments to the location with respect to the roadway is moved from 100 ft reference noise level. In most cases, these adjustments will to 200 ft. Traffic noise levels, in general, decrease at a rate be negative, thus providing attenuation to the reference of between 3 and 6 dB for doubling of observer distance. noise level. For instance, consider that the roadway of the The model considered in this study, through the use of example is now elevated above the surrounding terrain by the defined parameters, allows for five types of adjustments 41 for each road element, as shown in Figure 1. The distance The complete method uses all the parameters discussed and vertical configuration adjustments are the most impor- in this section and applies them to compute a complete set tant of these in terms of frequency of occurrence and model of adjustments. Thus, under the restrictions of the model sensitivity. used in this study, this method represents the more exact For the general case then, each roadway element gives solution. It precedes the short method in the guide because two reference noise levels (one for autos, one for trucks) it is felt that an understanding of the complete method is based on the infinite element length assumption and using necessary before the short method can be used. the traffic parameters. These reference noise levels for each The short method, shown in lighter type in Figure 1, element are then modified by the applicable adjustments allows the designer to obtain a quick, first approximation and, finally, the sum of all corrected noise levels (adding to the expected noise levels. In general, this procedure will contributions from all road elements) yields the desired result in higher noise levels than the complete method. final noise level at the observer position. If a potential high noise level is discovered, the complete solution should then be used to assess properly the mag- CRITERIA AND RESPONSE nitude of the problem; however, the method allows the designer to discard observer positions unaffected by the Once the expected noise level is computed at the observer roadway, resulting in considerable time savings. These location its meaning must be evaluated in terms of some savings result because only a limited amount of data is predetermined noise criteria. The criteria used in this guide required, and the calculations necessary to obtain the are presented and discussed in Section Six. If on the basis predicted noise levels are simplified by the use of tables. of these criteria it appears that the proposed highway design The user should be aware of the limitations of this tech- will be undesirably noisy or cause significant community nique. Because the guide was written with the general opposition, the highway engineer can reenter the Design traffic noise problem in mind, many generalizations had Guide with highway modifications and reevalaute the to be made. The use of these techniques for unusual cases situation. (i.e., very low vehicle volume) should be approached with care and understanding. However, for the general design COMPLETE AND SHORT METHODS case, where medium-to-large vehicular volumes are con- Sections Four and Five present the complete and short noise sidered by the highway designer, this guide is a reliable prediction methods, respectively. They are both shown approach, allowing the inclusion of traffic noise as a schematically in Figure 1. parameter in highway design.

SECTION FOUR—COMPLETE METHOD

The complete method for estimating the noise generated by SECTION 1—ROADWAY ELEMENT IDENTIFICATION a roadway at a selected observer location is given in this A roadway element is defined as that section of the road- section. A typical example is presented following the in- way whose cross-section and traffic flow characteristics can structions to more fully illustrate the method. The method be considered constant and that can be analyzed directly is divided into four main sections: by means of a straight infinite roadway noise model with Section 1—Roadway Element Identification: The a simple correction to allow for the angle subtended by the roadway is separated into elements with constant charac- element at the observer. teristics, thus simplifying the analysis. In many real cases the highway engineer will be able to identify the roadway with a single, effectively infinite and Section 2—Traffic Parameters Identification: Pa- straight, element. In other cases, however, analysis into rameters of speed and volume are computed, thus describ- two, three, or more elements will be required. The following the dynamics of the roadway elements. ing rules and procedures are set forth to help the process Section 3—Roadway Characteristics and Observer of element identification. Characteristic Identification: The geometrical characteris- To be defined as a roadway element, a section of roadway tics of each roadway element and the relationship of the must satisfy the following requirements: (1) firstly, all observer and each roadway element are established. lanes within the element must meet the requirements for Section 4—Noise Levels Estimation: Given the de- grouping together as a single equivalent traffic lane; (2) in scriptions from Sections 2 and 3 for each roadway element, addition, over the length of the element the conditions of this procedure shows how to calculate the desired Pre- unchanging cross section, straightness, unchanging gradient dicted Noise Levels for each element and finally how to and constant traffic operating conditions must be met. combine them to obtain an over-all noise level at the 1.0 WORK SHEET NO. 1 (Fig. A-4): The conditions and observer due to the entire roadway. All work sheets used requirements necessary to define the Roadway Elements in this procedure appear in Exhibit A. Figures and tables are presented here in detail. The procedure is as follows: used in this procedure appear in Exhibit B unless otherwise 1.1 On a route map of convenient scale select the ob- noted. server location for which analysis is required. 42

1.2 Draw a line from this location to intersect the road- Rules for Element Identification way at its nearest point (i.e., right-angle intersect). Lane Groupings: To permit lane grouping within a single 1.3 On either side of this intersect point mark off a element the following conditions must apply: length of roadway equal to four times the length of the observer-roadway intersect. i. All lanes must lie at the same elevation with respect Note: The length of road just defined to all intents and to the terrain. purposes can be considered as infinitely long. Sections of Lane and median separators must not shield lanes road further removed from the intersect point can be acoustically from each other. neglected unless their configuration is such as to render Vehicle operating conditions must be broadly similar them particularly noisy. for each lane. 1.4 Examine the cross section of the roadway at the (Most roadways satisfy these conditions, consequently all intersect point to determine the number of different lane roadway lanes can be accommodated within a single ele- groupings required (in accordance with the rules in Work ment. In general, however, these conditions do not permit Sheet No. 1). Denote these A, B, C, etc., starting with the frontage roads and ramps to be included with the main lane grouping nearest the observer. highway configuration.) Note: This lane grouping test simply allows for highway Alinement (Curves): To satisfy the requirements of a configurations having different pavement elevations in each single element definition the element must be effectively direction of flow, or having an acoustically opaque median straight. The following rules apply: barrier or berm. The designer is not advised to take frontage roads into account at this time because it will unduly Stretches of road separated by curves must, in general, complicate the processof element identification. be regarded as separate elements. 1.5 Study each lane grouping along its length with regard When the ratio of curve radius to observer distance to significant changes in alignment (curves), section, gradi- exceeds ten and when the observer lies within the triangle ent, or flow as defined in the work sheet. Identify by formed by the normal intersects of the roadway at the curve checking the appropriate box in the work sheet. tangency points, the curve itself should be represented by 1.6 Following the conditions set forth in the work sheet, a straight element to provide a "best fit" representation of identify and number those elements pertinent to each lane the curve. grouping Enter and describe these in the second table on A roadway having double or multiple curves can be the work sheet. represented by a "best fit" straight roadway as long as devia- Note: Elements that run the total length (8D) of the tions from this representation do not exceed ±20% of the roadway section are termed Infinite Elements. Elements mean observer-roadway distance. that extend across the 4D limit in one direction but which Gradients: To satisfy the requirements of a single-element terminate within the 8D roadway length are termed Semi- definition the element must not contain a change in roadway Infinite Elements. Elements that start and finish within the gradient of greater than 2%. 8D limits of the roadway are termed Finite Elements. Cross Section: To satisfy the requirements of a single- These three element classifications are numbered I, II, and element definition the cross section along the length of the III, respectively. element must be effectively unchanging. Significant changes 1.7 On the same table note the position parameters that are defined as follows: each element bears to the observer, as shown in Figure B-i. Note also the total pavement width, P. and the number of A change in the differential in roadway elevation with lanes appropriate to each. respect to the terrain (parameter H for elevated and depressed) of more than ± 10% about the midpoint value. Observer-Near Lane Distance (DN). Measured along A change in total roadway width (including median the right-angle intercept between the observer and the strip) of more than ±25% about the midpoint value. center of the near lane. A change, on the observer side of the roadway cut Element Length (L). This distance represents the distance or the roadway shoulder distance, for depressed length of the Road Element and must be measured in the and elevated configurations, respectively, of more than Finite Element case only. ±25% about the midpoint value. Angle 0. Angle 0 represents the included angle between observer and element in the Finite Element case and An exception to this requirement is the transition length of the included angle between observer and the Semi-infinite roadway between different roadway elevations (e.g., be- Element as shown in Figure B-i. (This angle can be posi- tween elevated and at-grade configurations). For such tive or negative.) Note that both angles are measured to the transitions the following rules apply: middle of the roadway. A transition section of roadway between an elevated and at-grade configuration or between a depressed and at- 1.8 Identify and describe any other roadway elements grade configuration is defined as having constant cross that you may wish to include at this time—parts of access section with a geometry corresponding to that of the mid- ramps, for instance. Identify each of these as a further lane point of the transition. grouping (D, E, etc.) and follow the general procedure of A transition section of roadway between an elevated steps 1.6 and 1.7. and depressed configuration (i.e., a transition that passes 43 through at-grade) is considered as two transitions, each of unknown, illustrative data from the "Highway Capacity them going to grade. Each of these transitions is analyzed Manual" are shown in Fig. C-i.) as above. 2.3 Enter the Vehicle Volume (V), in vehicles per hour, in Line 3. This is obtained by multiplying Line 1 by Line 2 Traffic Flow: To satisfy the requirements of a, single- and dividing by 100. element definition the traffic flow conditions along the 2.4 Enter Truck to Auto Mix in percentage of vehicle length of the element must be effectively constant. volume in Line 4. (If this is unknown, illustrative data Significant changes are defined as follows: from the "Highway Capacity Manual" are shown in Aflow volume change of ±10%. Fig. C-2.) An average speed change of ±10%. 2.5 Enter Truck Volume, in vehicles per hour, in Line 5. A change from uninterrupted to interrupted flow This is obtained by multiplying Line 3 by Line 4 and conditions. dividing by 100. 2.6 Enter Auto Volume, in vehicles per hour, in Line 6. With regard to the last item, interrupted flow imposed by This is obtained by subtracting Line 5 from Line 3. a traffic control signal is assumed to have an influence on 2.7 Enter expected Average Truck Speed, in miles per the operating noise of a vehicle over a distance of 1,000 ft hour, in Line 7 and the Average Auto Speed in Line 8. centered at the center of the signal area. This length would Note: The noisiest flow condition will occur under the therefore define the element length. condition of the highest stable volume flow at the highest Note: In principle at least, the highway engineer may expected average speed. The capacity chart of Figure C-3, thus develop noise estimates for complex roadway systems for instance, would suggest that the highest noise condition involving interchange and access ramps, intersections, front- on a highway designed for an average highway speed of age roads, etc. If too many elements are identified at one 70 mph, would occur with a lane volume close to 2,000 vph time, however, the procedure may become laborious. It is at an average speed of 45 mph. suggested that the user use judgment in determining those 2.8 Enter Lines 5 and 6 from Work Sheet No. 2 in sections of road and groupings of lanes that will influence Lines lb and 1 a, respectively, in the Parameter Work Sheet. the noise environment. Enter Lines 7 and 8 from Work Sheet No. 2 in Lines 2b 2.0 ROAD ELEMENTS: Elements defined on Work Sheet and 2a, respectively, in the Parameter Work Sheet. No. 1 in the Parameter Work Sheet (Fig. A-i) in the columns provided, one element per column, by noting: SECTION 3-ROADWAY CHARACTERISTICS AND The Road Element Number. OBSERVER CHARACTERISTICS IDENTIFICATION The Road Element Type. The applicable Time Interval of interest. This section describes the procedure for Roadway and Note: The Parameter Work Sheet can be used to handle Observer Characteristics identification and it covers Lines several Road Elements at one Time Interval, or one Road 3 through 10 in the Parameter Work Sheet (Fig. A-i). Element at several different Time Intervals. 1.0 FLOW CHARACTERISTICS: Note the Flow Character- istics of each Road Element by checking either Line 3a or SECTION 2-TRAFFIC PARAMETERS IDENTIFICATION Line 3b in the Parameter Work Sheet. Interrupted Flow is defined as the vehicle flow interrupted This section describes the procedure for Traffic Parameters by an outside source, such as STOP signs and traffic lights. Identification. It covers Lines 1 and 2 in the Parameter Slowdown or stop due to heavy traffic, accident, etc., is not Work Sheet. The procedure is as 'follows: an outside source. 1.0 VEHICLE OPERATING CONDITIONS: Determine the 2.0 PAVEMENT CHARACTERISTICS: Measure the Pave- Vehicle Operating Conditions for each Road Element at ment Characteristics for each Road Element and enter in the required Time Interval and enter in Lines 1 and 2 Line 4a and Line 4b in the Parameter Work Sheet. These in the Parameter Work Sheet. The Vehicle Operating data may be transferred from Work Sheet No. 1. Conditions are: 3.0 PERCENTAGE GRADIENT: Establish the Percentage The Vehicle Volume, V, in vehicles per hour. Gradient for each Road Element and enter in Line 5 in The Average Speed, S, in miles per hour. the Parameter Work Sheet. Percentage Gradient is defined as the change in roadway These parameters are required separately for two categories elevation measured in feet per 100 ft of roadway. Note that of motor vehicles-automobiles and trucks, as defined in a Percentage Gradient <2% is considered insignificant and Section One. is noted as 0%. If these parameters must be computed from estimates of 4.0 VERTICAL CONFIGURATION: Determine the form of AADT and of percentage flow and mix variations during Vertical Configuration for each Road Element and check the day, Work Sheet No. 2 (Fig. A-5) is provided. the appropriate line in the Parameter Work Sheet. 2.0 WORK SHEET NO. 2: For each Road Element identified and defined in Work Sheet No. 1: Elevated: When Road Element is elevated above the 2.1 Enter Estimated AADT in Line 1. immediate surrounding terrain. 2.2 Enter the Vehicle Volume, for the required Time Depressed: When Road Element is depressed below Interval as a percentage of AADT, in Line 2. (If this is the immediate surrounding terrain (cut). 44

3. At-grade: When Road Element is level with the ment Adjustment for each Road Element and enter in immediate surrounding terrain. Line 3 in the Noise Prediction Work Sheet. This adjustment is applicable to the Semi-Infinite Roadway Element 5.0 ROADWAY SURFACE: Determine the Road Surface and Finite Roadway Element only. For the Infinite Road- characteristics for each Road Element and check the way Element enter zero in Line 3. appropriate line in the Parameter Work Sheet. Smooth: Very smooth, seal-coated asphaltic pave- Semi-Infinite Element: Using the angle 0 (Line 8d in the Parameter Work Sheet) enter Figure B-6 and read ment. Normal: Moderately rough asphalt and concrete the appropriate adjustment in dB. The same adjustment applies for autos and trucks. surface. Rough: Rough asphaltic pavement with voids ½ in. Finite Element: Using the angle 0 (Line 8d in the or larger in diameter, or grooved concrete. Parameter Work Sheet) enter Figure B-7 and read the appropriate adjustment in dB. The same adjustment applies 6.0 POSITION PARAMETERS: Enter the Position Parame- for autos and trucks. ters from Work Sheet No. 1 for each Road Element. Evaluate and note the Observer-Equivalent Lane Distance, 4.0 GRADIENT ADJUSTMENT (): The Gradient Adjust- DE, using Fig. B-2. ment applies only for trucks and should be determined 7.0 SHIELDING EFFECTS: Determine the Shielding Effects whenever the gradient is greater than 2% (see Line 5 in between the observer and each Road Element and check the the Parameter Work Sheet). The appropriate adjustment appropriate line as follows: is obtained from Table B-i. Enter adjustment in Line 4 in the Noise Prediction Work Sheet under Truck. Barriers: Defined as infinite or finite barriers and walls generally located near the roadway and parallel to it. 5.0 VERTICAL ADJUSTMENT (): Determine the Verti- Buildings: This category includes residential, com- cal Adjustment for each Road Element and enter in Line 5 mercial, and industrial buildings that may wholly or par- in the Noise Prediction Work Sheet. This adjustment is tially shield the roadway from the observer. zero for an at-grade road configuration; otherwise, go to the Others: This category includes all other shielding procedure on Work Sheet No. 3 (Fig. A-6). effects, such as trees and vegetation. Terrain effects are not 6.0 WORK SHEET NO. 3: The procedure for estimating included. the Adjustment due to Vertical Configuration is as follows None: When no shielding is present. for each element: 6.1 Enter Road Elements defined in Work Sheet No. 1. 8.0 TERRAIN EFFECTS: Determine the Terrain Effects at 6.2 For an elevated road configuration, proceed through the observer by noting the observer elevation relative to the steps 6.4 through 6.10. ground elevation at the roadway and enter in Line 10 in the 6.3 For a depressed road configuration proceed through Parameter Work Sheet. steps 6.11 through 6.17. 6.4 Enter Height of Elevated Roadway, H1, in feet, in SECTION 4-NOISE LEVELS ESTIMATION Line 1. This section describes the procedure to obtain the Estimated Note: For an elevated roadway, H1 is defined as the Noise Levels at the observer due to the proposed highway height of the roadway element above the observer. If the using the data from the foregoing sections. observer is above the roadway elevation, this is considered 1.0 REFERENCE L50 AT 100 FT: Determine the Refer- an at-grade situation and no vertical adjustment is ence L50 Levels at 100 ft for both autos and trucks using necessary.

Figure B-3 and B-4 and enter in Line 1 in the Noise Pre- 6.5 Enter Observer-Equivalent Lane Distance, DE, in diction Work Sheet (Fig. A-2). These levels are obtained Line 2 (see Line 8b in the Parameter Work Sheet). as follows: 6.6 Enter Observer-Shoulder Distance, D, in Line 3. 1. Automobiles: Using Vehicle Volume, VA (Line la 6.7 Compute parameter A = H12/D2 and enter in Line 4. in the Parameter Work Sheet), enter Figure B-3 and read 6.8 Compute parameter B = H12! ( DE - D) and enter the corresponding sound level in dBA. in Line 5. 2. Trucks: Using Vehicle Volume, V, and Average 6.9 Using parameters A and B, enter Figure B-8 and Speed, S, enter Figure B-4 and read the corresponding read the appropriate adjustment for Elevated Roadway. sound level in dBA. Enter in Line 1 la. 2.0 DISTANCE ADJUSTMENT (): The distance adjust- 6.10 To obtain the adjustment for trucks, add +5 dB to ment to account for Observer-Near Lane Distance and the Line 1 ia and enter in Line 1 lb. (Note: the numerical Width of Road Element must be determined for each Road value of the truck adjustment is smaller than that for autos Element and entered in Line 2. This adjustment is the same but it can never be positive.) for autos and trucks and is obtained as follows: using Near 6.11 Enter Depth of Depressed Roadway, H21 in feet, Lane Distance, DN (Line 8a in the Parameter Work Sheet), in Line 6. and Road Element Width, P (Line 4a in the Parameter 6.12 Same as 6.5. Enter in Line 7. Work Sheet), enter Figure B-5 and read the adjustment 6.13 Enter Observer-Cut Distance, D, in Line 8. in dB. 6.14 Compute parameter A = H,21 (DE - D0) and enter 3.0 ELEMENT ADJUSTMENT (i 2 ): Determine the Ele- in Line 9. 45

6.15 Compute parameter B = H22/D0 and enter in the closest value to the one calculated in Line 6. Enter this Line 10. adjustment in Line 10. Go to step 9.10. 6.16 Using parameters A and B, enter Figure B-8 and 9.9.5 Enter Included Element Angle 0 in Line 11. This read appropriate adjustment for Depressed Roadway. Enter is obtained from Line 8d in the Parameter Work Sheet. in Line 12a. 9.96 Enter Included Bairier Angle a in Line 12. This 6.17 Same as 6.10 and enter in Line 12b. angle represents the included angle between the observer 7.0 SURFACE ADJUSTMENT (): Determine the Surface and the barrier. Adjustment for each Road Element and enter in Line 6 in 9.9.7 Compute the parameter A = (a/9O - 0) and enter the Noise Prediction Work Sheet (Fig. A-2). This adjust- in Line 13. ment is obtained from Table B-2 using the Road Surface 9.9.8 Using Parameter A and the Infinite Barrier Adjust- classification from Line 7 of the Parameter Work Sheet ment (Line 6) enter Figure B-9 and read the appropriate (Fig. A-i). adjustment for a finite barrier. Note that the adjustments 8.0 SHIELDING ADJUSTMENT (A6 and 7 ): Determine are given for only three values of the Infinite Barrier. Select the Shielding Adjustments for each Road Element and enter the closest value to the one calculated in Line 6. Enter this in Line 7a or Line 7b of the Noise Prediction Work Sheet adjustment in Line 14. Go to step 9.10. as follows: 9.9.9 Enter Included Barrier Angle a in Line 15. This angle represents the included angle between the observer If Line 9d in the Parameter Work Sheet is checked, and the barrier. the shielding adjustment is zero. Proceed to step 10.0. 9.9.10 Compute the parameter A = a/ 180 and enter in Otherwise, go to the procedure on Work Sheet No. 4 Line 16. (Fig. A-7). 9.9.11 Using parameter A and the Infinite Barrier Ad- 9.0 WORK SHEET NO. 4: The procedure for estimating justment (Line 6) enter Figure B-9 and read the appropriate Shielding Adjustments due to barriers, buildings and other adjustment for a finite barrier. Note that the adjustments effects is as follows for each element: are given for only three values of Infinite Barrier. Select the 9.1 Enter Road Elements defined in Work Sheet No. 1. closest value to the one calculated in Line 6. Enter this 9.2 If Line 9a in the Parameter Work Sheet is checked, adjustment in Line 17. proceed to steps 9.4 through 9.10. 9.10 Enter the Finite Barrier Adjustment in Line 7a of the Noise Prediction Work Sheet (Fig. A-2). Note that the 9.3 If Line 9b or/and Line 9c on the Parameter Work algebraic addition of the Vertical Adjustment (4) Line 5 Sheet is checked, proceed to steps 9.11 through 9.13. and the Barrier Adjustment (6) Line 7a should not exceed 9.4 Enter Height of Barrier, H, in feet, in Line 1. -15 dB. ( + A > -15 dB.) 9.5 Enter Observer-Barrier Distance, DB, in feet, in 9.11 Multiple rows of intervening buildings and struc- Line 2. tures, such as houses and apartments, will reduce levels by 9.6 Enter Equivalent Lane-Barrier Distance, R11, in feet, up to 10 dB, depending on the degree of shielding provided. in Line 3, where RB = (DE - DE). A single row of houses between the roadway element and 9.7 Compute the ratios H2/DB and H2/RB and enter in the observer generally will reduce levels by approximately Lines 4 and 5, respectively. 5 dB. Enter the assumed adjustment in Line 18 in Work 9.8 Using these ratios, enter Figure B-9 and read the Sheet No. 4. Note that this adjustment is always negative. appropriate adjustment for an Infinite Barrier and enter in 9.12 A design value of 5-db noise reduction for every Line 6. 100 ft of foliage between the observer and the roadway 9.9 Depending on the Road Element type considered, element may be used if the trees are at least 15 ft tall and do one of the following: sufficiently dense so that no visual path between them and For a Finite Roadway Element proceed to steps 9.9.1 the roadway exists. The total adjustment should not exceed through 9.9.4. 10 dB. Enter the assumed adjustment in Line 19 in Work For Semi-Infinite Roadway Element proceed to steps Sheet No. 4. Note that this adjustment is always negative. 9.9.5 through 9.9.8. 9.13 Add the adjustments of Lines 18 and 19 and enter For Infinite Roadway Element proceed to steps 9.9.9 in Line 20. Enter this adjustment in Line 7b in the Noise Prediction Work Sheet. through 9.9.11. 10.0 L50 AT OBSERVER: Determine the L50 Level at the 9.9.1 Enter Included Element Angle 0 in Line 7. This observer for each Road Element and enter in Line 9 in the is obtained from Line 8d in the Parameter Work Sheet. Noise Prediction Work Sheet. This is obtained by alge- 9.9.2 Enter Included Barrier Angle a in Line 8. This braic addition of Lines 1 and 7. angle represents the included angle between the observer 11.0 L10 - L50 ADJUSTMENT: Determine the L10 adjust- and the barrier. ment for each Road Element and enter in Line 10 in the 9.9.3 Compute the parameter A = (a/ 0) and enter in Noise Prediction Work Sheet. This is obtained by using Line 9. Work Sheet No. 5 (Fig. A-8) and the following procedure: 9.9.4 Using parameter A and the Infinite Barrier Adjust- 12.0 WORK SHEET NO. 5: The procedure for estimating ment (Line 6) enter Figure B-9 and read the appropriate the L10 adjustment is as follows for each element: adjustment for a finite barrier. Note that the adjustments 12.1 Enter Road Element, defined in Work Sheet No. 1. are given for only three values of the Infinite Barrier. Select 12.2 Enter Vehicle Volume, V, in Line 1. This is ob- 46 tamed from Lines la and lb in the Parameter Work Sheet Element 1 is a Semi-Infinite type, and is represented for autos and trucks, respectively. by the at-grade cross section No. 1. 12.3 Enter Average Speed, S, in Line 2. This is obtained Element 2 is a Finite Element type and is represented from Lines 2a and 2b in the Parameter Work Sheet for by depressed cross section 2. autos and trucks; respectively. Element 3 is a Semi-Infinite type and is represented 12.4 Enter Observer-Equivalent Lane Distance, DE, in by depressed cross section 3. Line 3. This is obtained from Line 8b in the Parameter Work Sheet. With the road elements identified, the procedure for Traffic Parameters Identification and Roadway Characteristics and 12.5 Calculate parameter A = VDE/S, and enter in Line 4. Observer Characteristics Identification is used to obtain all the necessary parameters and complete the Parameter Work 12.6 Using parameter A, enter Figure B-10 and read Sheet (Fig. 6). The Reference Noise Levels and the neces- appropriate adjustment in dB. Enter in Line 5. sary adjustments are found by following the Noise Level INTERRUPTED FLOW ADJUSTMENT: Determine the 13. Estimation procedure. The results are shown on the Noise Interrupted Flow Adjustment for each Road Element and Prediction Work Sheet (Fig. 7). Note that the vertical enter in Line 11 in the Noise Prediction Work Sheet. This adjustment for roadway element 1 is zero because there is adjustment applies only if Line 3b in the Parameter Work an at-grade condition; however, roadway element 2 is de- Sheet is checked. The adjustment is obtained from pressed and the vertical adjustment for trucks is also zero. Table B-3. This result• is easily explained by following the procedure 14.0 L10 AT OBSERVER: Determine the L10 Level for for Work Sheet No. 3 (Fig. 8). Note that the depression each Road Element and enter in Line 12 in the Noise depth is only 5 ft; thus, in reality, the trucks whose noise Prediction Work Sheet. This is obtained by algebraic source (mainly the exhaust stack and engine) is elevated are addition of Lines 9, 10, and 11. not shielded from the observer. Figure 10 shows the L10 15.0 ELEMENT TOTAL: Determine the Element Total for adjustment. each Road Element and enter in Line 13. This is obtained The final L50 and L10 Noise Levels are shown to be for both the L50 and L10 Levels by adding the levels for 57 dBA and 59 dBA, respectively. This is shown in automobiles and trucks. The procedure for adding decibel Figures 11 and 12, respectively. The meaning of these levels is presented in Work Sheet No. 6 (Fig. A-9). (A levels as compared against the Noise Criterion is discussed sample calculation is given in Table B-4.) in Section Six. 16.0 GRAND TOTAL: Determine the Grand Total L50 Predicted Noise Levels by adding the contributions from all roadway elements and enter in Line 14. Do the same SECTION FIVE-THE SHORT METHOD for L10 Predicted Noise Levels. Again follow the procedure In the previous section, the step-by-step procedure of pre- in Work Sheet No. 6. dicting noise levels from a roadway is presented. However, 17.0 L10 - L50: Determine the L10 - L50 Predicted when one approaches the problem of noise prediction from Noise Level and enter in Line 15 in the Noise Prediction an existing or proposed roadway, it is desirable first to Work Sheet. This is obtained by algebraic difference of the obtain a rough idea of the magnitude of noise levels ex- Grand Total L10 and L50 Levels. pected and to compare those with design criteria. To this purpose, the short method presented in this section was Illustrative Example developed. This method uses some of the procedures from To more fully illustrate the foregoing procedure, a typical Section Four. example is presented and solved in full. This same example It should be noted at this point that the short method is later solved using the short method in Section Five. should not be used in lieu of the complete method analysis Consider a roadway configuration as shown in Figure 2. and that it is restricted to fairly simple roadway configura- The observer is located in a classroom, 400 ft from the tions. Properly used, however, it allows the designer to nearest lane of the roadway. At the time of interest, 8 to pin-point trouble areas quickly and, in many cases, to 10 AM, the average speed of traffic flow is estimated to be reduce the analysis time by discarding unaffected observer 55 mph, with a truck/auto mix of 5%. In addition, it is positions. estimated that the AADT is 49,000 vpd, of which 7% per hour will pass between 8 to 10 AM. The problem is to PROCEDURE calculate both the L50 and the L1.0 Predicted Noise Levels using the complete method. The first task in the procedure Basically, the method assumes that the roadway can be is the roadway element identification. Using Work Sheet approximated by one infinite element with constant traffic No. 1 (Fig. 3), note that, according to the rules, there is parameters and roadway characteristics; the assumed road- only one lane grouping (in this case, eight lanes of traffic way geometry is shown in Figure 13. The work sheets used with a 20-ft median strip) but that a single infinite roadway in this procedure appear in Exhibit A. Figures and tables element cannot be assumed, because there are both align- used in this procedure appear in Exhibit B unless otherwise ment and cross-sectional changes. Using the procedure of specified. The procedure is as follows: Section 1, three roadway elements are identified as shown 1.0 ROAD ELEMENT: Draw a line from the observer in Figure 3 and Figure 5. They are: location to intersect the roadway at its nearest point (i.e., 47

PLAN VIEW OF PROPOSED HIGIfWAY AND SURROUNDINGS. 10' STA STA STA STA to STA 200 ___250______300

STA 400 STA 150 350

STA STA ---1Residential 400 ----- I chool I I I -Observer Location I I I ------

NOTE; All Dimensions are in Feet CROSS SECTION NO. 1 Not Drown to Scale Up to Station 200 4 Lanes c. Median Strip Emergency Lane / 4Lanes / - Emergency Lane Level ). 1'.

10 48 20 48 10 L Obser )C lr F 116 136 CROSS SECTION NO. 2 STA 200 through 300 Observer Location c A Gnd Level 2:1 3:1 5 I 10 Same as Above 15 CROS9 SECTION NO. 3 From STA 300 Observer Location Gnd Level 74 c 7 '>2.51 2:1 :

37.5 4s Same as Above 30 Figure 2. Typical example of a pro poied highway.

right-angle intersect). This defines the position of the server and infinite roadway element at the nearest point. assumed infinite roadway element. Enter in Line 8a in the Parameter Work Sheet. 2.0 VEHICLE OPERATING CONDITIONS: Determine the 5.0 REFERENCE L50 AT 100 FT: Determine the Reference Vehicle Operating Conditions for the infinite road element L50 Levels at 100 ft for both autos and trucks (using Fig- by using the Traffic Parameters at the roadway nearest ures B-3 and B-4) and enter in Line 1 in the Noise Predic- point (if these parameters vary along the roadway) and tion Work Sheet (Fig. A-2). These levels are obtained as follow the procedure for Work Sheet No. 1 (see Section follows: Four). Enter these data of the Parameter Work Sheet Automobiles: Using Vehicle Volume, VA (Line la (Fig. A-i) in Lines 1 and 2. in the Parameter Work Sheet), and Average Speed, SA, 3.0 VERTICAL CONFIGURATION: Determine the form of enter Figure B-3 and read the corresponding sound level Vertical Configuration at the roadway nearest point and in dBA. check the appropriate line in the Parameter Work Sheet. Trucks: Using Vehicle Volume, VT, and Average 4.0 PoSITION PARAMETER: Determine the distance to the Speed, Sq,, enter Figure B-4 and read the corresponding nearest lane (Dr) by measuring the distance between ob- sound level in cIBA. WORK SHEET NO. 1 WORK SHEET NO.2 ROAD ELEMENT IDENTIFICATION TRAFFIC FLOW PARAMETERS Lane Grouping Change in Line Number 1 2 3 Group ROAD ELEMENT DESCRIPTION Alinement Section Gradient Flow l I Type II III II lane roadway with a 8_1c 8-ia 8 7R,f. TIME INTERVAL 8-la A 20 foot median strip _____ m. 1 1 Estimat.d AADT, Vehicles per Day 119000 19000 119000

2 Fig Cl Vehicle Volume, % AADT 7% 7% 7%

3 V Vehicle Volume, vph 7000 7000 7000

4 Fig C2 Truck/Auto Mix, % 5% 5% 1 5% 5 VT Truck Volume, vph 350 350 350

6 f1 Auto Volume, vph 6650 6650 6650 Lane Group Position Parameters Element No. DESCRIPTION Pavement 7 ST Fig C3 Average Truck Speed, mph 55 55 5 -- Iype D L 9 P N 8 Fig C3 Average Auto Speed, mph 55 55 5 II STA 100 through 200 590' - 19 116' 8 SA on level roadway Figure 4. Work Sheet No. 2 for illustrative example (complete method). STA through 2 1 200 300 on depressed roadway 395' 1000' 102.5° 116' 8

STA 300 through 100 II 590' - 19 116' 8 3 on depressed roadway

* Element Type Classification: Type I Infinite Element It Semi-Infinite ill Finite Figure 3. Work Sheet No. 1 for illustrative example (complete method). ROADWAY ELEMENTS

DADAkATR WRk cHFFT 100 Number 0 ROAD ELEMENT 1 2 3 Type II III II i-10 -10 8-iu TIME INTERVAL V Observer i VEHICLE VOLUME (a) AutomobIles 6650 6650 6650 1 - (vp)h 2 (b) Trucks - -T - 350 350 350 ROADWAY ELEMENT NO. 1 Automobiles 55 55 55 Type: Semi-Infinite < 2 S AVERAGE SPEED 2 (mph) DN 590 Feet Trucks 55 55 55 P = 116 Feet * N 8 Lanes FLOW Uninterrupted 1= 19.0° 0 CHARACTERISTIC * a1 = 71.0° Interrupted DB = 330 Feet (a) Width (P) RB = 312 Feet 116 116 116 PAVEMENT uJad 1 Observer (b)No.of Lanes (N) 8 8 8 * PERCENTAGE GRADIENT ' 5 (If greater than 2%) 0 0 0 U ROADWAY ELEMENT NO. 2 - - * - (a) Elevated 6 VERTICAL * c CONFIGURATION (b) Depressed / - (c) At-Grade - - * (a) Smooth DN 7 ROAD SURFACE Normal Type: Finite * Rough DN = 395 Feet = = = = (a) D (ft.) Ubserver L = 1000 Feet 590 395 590 P= 116 Feet CA WS. POSITIONS DE (ft.) 642 N = 8 Lanes 8 642 .50 I- 1 PARAMETERS = 102.5° L (ft.) - 1000 - 'Li I-. 9 ROADWAY ELEMENT NO. 3 (dig.) * 19.0 102.5 19.0 (a) Barrers * Type: Sml Infinite 9 SHIELDING Buildings / o EFFECTS * DN 590 Feet cc Others uJ * P = 116 Feet Nons 1/ N = 8 Lanes '/' 0 = 19.0 TERRAIN O 10 0 ID 0 - EFFECTS Observer c -— - * Check Where Applicable

Figure 5. Identified roadway elements showing applicable parameters (complete method) Figure 6. Parameter Work Sheet for illustrative example (complete method). NOISE PREDICTION WORK SHEET

Line L Number 1 2 3 ROAD ELEMENT I Symbol ( Te II III II TIME INTERVAL 8-_1 8-10 L.m. 8-10 a.m. - - Ff— VEHICLE TYPE Auto Truck Auto Truck Auto Truck Auto Truck 1 I I Reference L50 at 100 ft 72 69 72 69 72 69 1 2 All - DIstance -11 -11 - 9 - 9 -11 -11 32,.- Element - - -2-2 - - v 4 3 - GradIent U --- o 0 0 0 0 0 5 & S. VertIcal 0 0 - 5 0 -114 - 9 45 --6 Surface 0 0 0 0 0 0 LU 7 4 wS. ______14 14 0 0 0 - LShlelding (a) Barriers - _- 0 4; 4 < 1(b) Structures & Plant. 5 5 5 5 0 0 4 - — - - - - 8 TOTAL ADJUSTMENT _211 _214 -21 -16 -29 -24 I (add rows 2 throuah 7) L50 AT OBSERVER U 9 145 (add row 1 to row 8 148 51 53 143 145 U --- ) 1- 10 WS. 10 - L50 ADJUSTMENT + 1 + Li + 1 + Ii + 1 + !t

INTERRUPTED ADJUSTMENT 0 11 4 12 LjO AT OBSER9R - - (add row 10& 1 to row 9) 149 49 52 57 1414 149 - 50 147 13 V.S. ELEMENT TOTAL [L50L10 55 52 58 50

14 V$ GRAND TOTAL L = 57 dBA L10 = 59 dBA

15 L10 - L = 2 dBA

Figure 7. Noise Prediction Work Sheet for illustrative example (complete method).

> -c C 2 C Lr\ CJ 1( C .21 0

I-I 0 0 E '0

C 22 0

Lt • • fT >0 . I-I (flU.' Uu, UJ _5 I f D 4 CC a

-.--- C c C'1- 2'U '- z c i \I 4 o ' J J I, II J J II 41 2o 0 0 < o 0 0 4 I C ------ - a-a_--. _JC ujO o , AVM33111 Q1VA13 AYM33114 aassia W4 04 U . co am U..22 U c IL.= j 00 ii iuu I - c, 51

WORK SHEET NO. 4

Lin. Num b.r 1 - 2 - - ROADWAY ELEMENT II _III Symbol F Type Ref. TIME INTERVAL 8-1a. n.8-10 10 1 H - Height of Barrier 2 1)8 - Observer - Barrier Distance Equivalent Lone - Barrier Distance 3 RB - 0.3 4 - H21'1B 0.32 5 H2/8 -6 . 0 6 = FigB9 Adiustmentfor Infinite Barrier

- be Included Element Angle 7 0 LU —C 8 a Included Barrier Angle —< cE 9 ! A=a/9 UJ UJ Ce < —10 — Adjustment In dB • Comp. Element Angle 19.0

12 Of • Included Barrier Angle 71.0 13 '° A=c(/90-e pg 14 — Fig 89 ui P Adjustment in dB _.L tIncluded Barrier Angle .! ---n .-• 16 -, CE A=a/180 ---a • 17 — Fig 89 < .EM Adjustment in dB

LA LU Multiple Rows of intervening Bldgs and Structures, Such As Houses, Apartments, 18 etc. Will Reduce Levels By Up To U 10 dB -5 Assumed Adjustment in dB -5

A Design Value of 5 dB Noise Reduction For Every 100 ft of Pionting (Depth) May Z Be Used If These Trees Are At Least 15 ft 19 Toil and Sufficiently Dense So That No Z Visual Path Between Them and The Highway Exists Assumed Adjustment in dB

Total Adjustment for Structuti 20 and Planting (Add Lines 18 - T- and 19) 5 Equivalent Lane Location

Barrier

1DN 7 N DB

Observ.r Location -- '

Finite Roadway Element Semi Infinite Roadway Element Figure 9. Work Sheet No. 4 for illustrative example (complete method). 52

WORK SHEET NO. 5 1- 10 ADJUSTMENT

Line I Number 1 2 3 ROAD ELEMENT I Symbol Type ii iii II TIME INTERVAL Ref. 8-10 a.m. 8-10 a.m. 8-10 a.m. VEHICLE TYPE Auto Truck Auto Truck Auto Truck Auto Truck

1 V P.WS, Vehicle Volume, vph 6650 350 6650 350 6650 350

2 S P.WS. Average Speed, mph 55 55 55 55 55 55

3 D P.W.S. Observer - Equiv. Lane Distance, ft. 642 6142 450 450 642 642

4 A Parameter A=VDE/S, Vehicles ft/rn 77500 4070 54500 2860 7750o 14070

Flg.B10 1.10 Adlustment, dB +1 +14 +1 +11 +1 +14

Figure 10. Work Sheet No. 5 for illustrative example (complete method).

WORK SHEET NO. 6 DECIBEL ADDITION

Antilog Table Sourc. or Sound Antilog Columns - Left Digit of Sound Level Right Digit of Element No. Level - dB ------Antilog 9 8 7 6 5 4 3 2 Sound Level

1 L 50 50 1 0 0 0 0 1000 2 L50 55 - 3 1 6 2 1 1259 3 L50 47 - - - - 5 0 1 2 1585 3 1995

4 2512

5 3162

6 3981

7 5013

8 6311 Total 57 -- - - 14 6 6 3 9 7944

List sound levels by source or Roadway Elements. Enter antilog table with right digit of sound level to obtain antilog value Enter antilog on work sheet under antilog Columns. Position by entering left digit of antilog under the column numbered the same as the left digit of the sound level. Add the antilog values of the Individual sources to obtain the antilog of the total sound level. Enter antilog table with antilog of total sound level. Obtain right digit of total sound level by selecting digit from table whose antilog is closest numerically to the antilog obtained in Step 4. lndentify column number containing left most digit of the antilog derived from Step 4. This is the numerical value of the left digit of the total sound level. Figure 11. Work Sheet No. 6 for illustrative example (complete method). 53

WORK SHEET NO. 6 DECIBEL ADDITION

Antilog Table Source or Sound Antilog Columns - Left Digit of Sound Level - RI9li Digit of EIem.nt No. L.v.l - dB - - - - Antilog 9 8 7 6 5 4 3 2 Sound Level

1 L10 52 - - - - 1 5 8 5 0 1000

2 L10 58 - - - 6 3 i i 1 1259

3 L10 50 - - - 1 0 o 0 2 1585

3 1995

4 2512

5 3162

6 3981

7 5013

8 6311

Total 59 - - - 9 6 1~~

List sound levels by source or Roadway Elements. Enter antilog table with right digit of sound level to obtain antilog value. Enter antilog on work sheet under antilog Columns. Position by entering left digit of antilog under the column numbered the same as the left digit of the sound level. Add the antilog values of the Individual sources to obtain the antilog of the total sound level. Enter antilog table with antilog of total sound level. Obtain right digit of total sound level by selecting digit from table whose antilog is closest numerically to the antilog obtained in Step 4. Indentify column number containing left most digit of the antilog derived from Stop 4. This is the numerical value of the left digit of the total sound level. Figure 12. Work Sheet No. 6 for illustrative example (complete method).

6.0 DISTANCE ADJUSTMENT: Determine the Distance 7.0 VERTICAL ADJUSTMENT: Determine the Vertical Adjustment to account for Observer-Near Lane Distance Adjustment and enter in Line 5 in the Noise Prediction and the Width of the Roadway and enter in Line 2 in the Work Sheet. This adjustment is zero for an at-grade con- Noise Prediction Work Sheet. This adjustment is the same figuration (if Line 6c in the Parameter Work Sheet is for autos and trucks and is obtained using the Near Lane checked); otherwise, do one of the following: Distance, DN (Line 8a in the Parameter Work Sheet), and entering in Table B-6. Find the closest DN listed and read 1. For an elevated roadway configuration, take height H the corresponding adjustment. and enter in Table B-7 for the appropriate adjustment.

4-Lane Traffic

Emergency Emergency Lane Lane I . ç73J/I/f/I'/I[ r •• .-: If / /1/ / id 4w--,L- 24''F 48

—140' Figure 13. Assumed roadway gross section (short method).

2. For a depressed roadway configuration, take depth H lane from the observer location is found at 400 ft. Through and enter in Table B-8 for the appropriate adjustment. this point one passes an infinite roadway element, as shown 8.0 L 0 AT OBSERVER: Determine the L50 Level at the in Figure 14. The roadway cross section at the nearest lane observer by the algebraic sum of Lines 1, 2, and 5 in the location corresponds to cross section 2 (a 5-ft depressed Noise Prediction Work Sheet. Enter in Line 10. roadway). This cross section is assumed valid for the entire 9.0 INFINITE ELEMENT TOTAL: Determine the infinite element. Following the procedure for the short method, a element total noise level at the observer and enter in Line 15 final Predicted Noise Level L50 of 61 dBA is found. This in the Noise Prediction Work Sheet. This is obtained by is shown in Figures 15 and 16. Note that the L50 noise level adding the L50 noise levels for autos and trucks, using Work obtained by this method is 4 dB higher than the complete Sheet No. 6 (Fig. A-9). method solution. In general, unless the roadway geometry Illustrative Example is very complicated, the short method will result in a higher Apply the short method described previously to the illus- value. The interpretation of both the Section Four results trative example of Section Four. In this case, the nearest and the foregoing results is discussed in Section Six.

PLAN VIEW OF PROPOSED HIGHWAY AND SURROUNDINGS. STA STA to STA 10' 250 STA 200 STA 300 STA 400 STA ____f ------— 350 [[ STATA00 ile STA 1 ResidentIal 400 rJ chool I / Oeer Location I I ------

NOTE; All Dimensions are in Feet CROSS SECTION NO. 1 Not Drawn to Scale Up to Station 200 4 Lanes Median Strip Emergency Lanes Emergenc y Lane Ground Level

48—a 116 136 CROSS SECTION NO. 2 STA 200 through 300 ç Obs.rv.r Location Gnd Level 7777T)2:

10 4 Some ci's Above P1 15 CROSS SECTION NO. 3 From STA 300 Obs.ryer Location Gnd Level

2.5:1 2. 1Z 157 I I .5- 41 37.5 Same as Above 4, 30 Figure 14. Typical example of a proposed highway showing short method approximation. 55

PARAMETER WORK SHEET

Number 1 ROAD ELEMENT ______Type i - TIME INTERVAL 8-10 - --- V1 (°) Automobiles 6650 w VEHICLE VOLUME ' 2 (vph) T (b) Trucks 350 U H SA Automobiles 55 2 Vs AVERAGE SPEED 2 (mph) - ST - Trucks 55 - * FLOW (a) Uninterrupted 3 CHARACTERISTIC * (b) Interrupted

(a) Width (P) 116 4 PAVEMENT w I- isl (b)No.of Lanes (N) 8 - * PERCENTAGE GRADIENT = 5 (If greater than 2%) * (a) Elevated 6 VERTICAL 0 CONFIGURATION (b) Depressed / * 0 - (c)At Grade - * (a) Smooth 7 ROAD * Normal SURFACE * Rough

(a) D (ft.)

8 VS POSITIONS DE (ft.) 1155 • PARAMETERS L (ft.)

I- (d)Q(d.9.) (a) Barriers * * = 9 SHIELDING Buildings 0 EFFECTS Others * >Uj ce - d) None LU - cc O TERRAIN F]o- - - EFFECTS * Check Where Applicable Figure 15. Parameter Work Sheet for illustrative example (short method).

SECTION SIX—COMPARISON WITH CRITERIA Criteria Work Sheet (Fig. A-3). Note the appropriate time AND INTERPRETATION interval applicable. 1.1 DESIGN CRITERIA LEVEL: Determine the Design Cri- This section takes the estimated outside traffic levels calcu- terion Level (L50 or L10) applicable by the following: lated in Sections Four and Five and tests their compatibility with the Design Criteria given in Table B-S. If L1.0 - L50 6 dB, then L50 Design Criterion applies. PROCEDURE If L10 - L50 6 dB, then L10 Design Criterion applies. The following is a step-by-step procedure: L1 - L50 is obtained from Line 15 in the Noise 1.0 CRITERIA WORK SHEET: Identify the observer cate- Prediction Work Sheet (Fig. 7). gory considered from Table B-9 (i.e., residences, inside; churches, etc.) by number and enter in a column in the This determines the Design Criteria levels to be used 56

NOISE PREDICTION WORK SHEET Line Number ROAD ELEMENT

5Ymo1 Type TIME INTERVAL 8-10 a.m. Ref. - VEHICLE TYPE Auto Truck Auto Truck Auto Truck Auto Truck - -

1 Reference L50 at 100 ft 72 69 2 LI = - Distance -10 -10 ,- Element

Gradient - - - - U—— - 5 Vertical & - 5 0 11 Surfac* - r WS. (a) Barriers 7 lding ° 7 (b) Structures & Plant. - - - - I TOTAL ADJUSTMENT 15 -10 (add rows 2 th.ouh 7) = U L50 AT OBSERVER 9 57 59 (add row 1 to row 8 ) U 10 WS. 1-10 - L50 ADJUSTMENT

- INTERRUPTED ADJUSTMENT O 11 U < 12 Lio AT OBSERVçR - (addrowO&1utorow9) - IL50 61 13 ELEMENT TOTAL

14 WS6 GRANO TOTAL L50 = 61 dBA L10 = dBA

15 L10 - -= dBA Figure 16. Noise Prediction Work Sheet for illustrative example (short method).

throughout the compatibility tests for that one observer 1.6 CRITERION DIFFERENCE OUTSIDE: Determine the cri- position and time interval only. terion difference outside and enter in Line 5 in the Criteria 1.2 ESTIMATED OUTSIDE TRAFFIC NOISE: Determine the Work Sheet. This is obtained by subtracting Line 3 from Estimated Outside Traffic Noise and enter in Line 1 in the Line 1. Criteria Work Sheet. This is obtained from Line 9 or 12 1.7 BUILDING NOISE REDUCTION: Determine the Build- in the Noise Prediction Work Sheet (Fig. 7), depending ing Noise Reduction and enter in Line 6 in the Criteria on the applicable design criteria. Work Sheet. This is obtained from Table B-9. Note that 1.3 AMBIENT NOISE LEVEL: Determine the L50 or L10 these noise reductions vary with geographic location and Ambient Noise Level in dBA at the observer location and open or closed window conditions. enter in Line 2 in the Criteria Work Sheet. Note that these 1.8 ESTIMATED TRAFFIC LEVEL INSIDE: Determine the levels are outside levels, independent of the observer Estimated Traffic Level Inside and enter in Line 7 in the category. Criteria Work Sheet. This is obtained by subtracting Line 6 Depending on the observer category, do one of the from Line 1. following: 1.9 INSIDE CRITERIA: Determine the L50 or L10 Inside Criterion in dBA and enter in Line 8 in the Criteria Work If observer category is 2, 4, or 7, do sections 1.4 Sheet. This is obtained from Table B-S. through 1.6. 1.11 CRITERION DIFFERENCE INSIDE: Determine the Cri- If observer category is 1, 3, 5, 6, 8, 9, or 10, do terion Difference Inside and enter in Line 9 in the Criteria sections 1.7 through 1.10. Work Sheet. This is obtained by subtracting Line 8 from 1.4 OUTSIDE CRITERION: Determine the L50 or L10 Out- Line 7. side Criterion in dBA and enter in Line 3 in the Criteria 1.12 COMPATIBILITY: Determine the Compatibility with Work Sheet. This is obtained from Table B-5. criteria and enter in Line 10 in the Criteria Work Sheet as follows: 1.5 AMBIENT DIFFERENCE: Determine the Ambient Dif- ference in dB and enter in Line 4 in the Criteria Work If Line 4 or S is :!~0 dB, enter YES. Sheet. This is obtained by subtracting Line 2 from Line 1. If either Line 4 or S is >0 dB, enter NO. 57

If Line 9 is :!~0 dB, enter YES. noise levels" that are compatible with speech requirements If Line 9 is >0 dB, enter NO. for a range of different land uses. Thus, based on the Design Criteria, the noise levels esti- The compatibility of an environment thus is based on mated for the roadway are judged as compatible or not these two considerations, as indicated in the Criteria Work compatible with the environment. Sheet. In order to assess the impact that can be expected when one or both of these considerations is exceeded NOISE IMPACT AND CRITERIA INTERPRETATION (No in Line 10 in the Criteria Work Sheet), three basic "noise impact" categories are defined: The idea of "acceptable noise level" implies no community reaction to an intruding noise source. In developing the No impact: Under this category, very little comment impact criteria for this •Design Guide, both the environ- or individual reaction is expected. mental conservation and environmental utility were con- Some impact: Under this category, some individual sidered. comment and reaction is expected but no group action is likely. The community in general will react if the existing Great impact: Under this category, strong individual noise environment is increased. As individuals, we have comment and group action may be expected. a natural urge to conserve what we already have. Thus, an increase in the existing noise levels due to a proposed Table B-10 relates these three categories to the amount by highway can be expected to produce some type of impact which the criteria are exceeded. on the community. Illustrative Example Irrespective of the increase in existing noise environment, the utility of an area depends on the ability to per- Using the criteria developed in this section, consider the form certain tasks. The tasks considered in this study are example discussed in Sections Four and Five. The results the ability to communicate (speech intelligibility) and of the short method gave a noise level of 61 dBA, and the sleep. Table B-S represents the "maximum acceptable complete method resulted in a noise level of 57 dBA. Let

CRITERIA WORK SHEET SHORT COMPLETE METHOD METHOD

V U OBSERVER CATEGORY 3 I- • 8-10 8-10 TIME INTERVAL .l w a.m. a.m.

1 Estimated Outside Traffic Level (dBA) 61 57

2 Ambient (dB) 55

- - T Outside Criterion (dBA) 55 55 B5

-- C Ambient Difference (dB) - (Subtract Line 2 from Line 1) 2

iterion Difference Outside (dB) 6 2 btract Line 3 from Line 1) F(sr, 6 T Building Noise Reduction (dB) 20 20 B8

7 UJ Estimated Traffic Level Inside (dBA) 141 37

- - 8 Inside Criterion (dBA) 140 140

terion Difference Inside (dB) 1.0 -3.0 btract Line 8 from Line 7) 9 rc(srui

Compatability No Yes 011

Figure 17. Criteria Work Sheet for illustrative example (complete and short method). 58

us now describe the utility of the area by locating the Thus, the criterion is exceeded by 1 dB. Figure 17 indi- observer inside the classroom. Assume the school in ques- cates that when the criterion is exceeded using the short tion is air-conditioned and located in Los Angeles. The method, a possible noise problem is present; thus, the ambient noise level outside the building was measured to complete method should be used. be 55 dBA. Find the impact of the proposed highway in The Estimated Traffic Noise Level Inside for the complete method results in a noise level of 37 dBA. Thus, the the classroom only. projected environment is compatible with criteria. Table B-5 indicates that the criterion for a classroom is Note that if the impact of the outside noise level was also 40 dBA. For the geographic area under consideration, required, the complete method shows that both Criterion Table B-9 gives a 20-dB attenuation between outside and Difference Outside and Ambient Difference are exceeded by inside for closed windows. 2 dB. In that case, the highway noise levels would not be Looking at the short method first one notes that the compatible and, checking Table B-b, one finds that some Estimated Traffic Level Inside will be 41 dBA (Fig. 17). impact would be expected.

EXHIBIT A PARAMETER WORK SHEET

WORK SHEETS Number ROAD ELEMENT Type _I u -- - - TIME INTERVAL V Automobfles v VEHICLE VOLUME 1 - (vp h) 2 Trucks u_ uj tLC S Automobiles 2 S AVERAGE SPEED < (mph) 2 Trucks ST * FLOW (a) Uninterrupted 3 CHARACTERISTIC * (b) Interrupted 12 —-— (a) Width (P) L11 4 iSJ PAVEMENT 04 U.' (b)No.of Lanes (N * PERCENTAGE GRADIENT X 5 (If greater than 2%) U - - * - (a) Elevated 6 VERTICAL * CONFIGURATION (b) Depressed * - - - (c) At—Grade (a) Smooth * 7 ROAD * SURFACE Normal * = = = = Rough (a) D (ft.)

LA V.S 8 POSITIONS DE () 1 PARAMETERS L (ft.) U.' e(d..) U * (a) Barriers * 9 SHIELDING Buildings = EFFECTS Others * U.' None * -- Ln TERRAIN O -7101 - - EFFECTS * Check Where Applicable 59

NO ISE PREDICTION WORK SHEET - Line Number ROAD ELEMENT Symbol Type TIME_INTERVAL - Ff- - VEHICLE TYPE Auto Truck Auto Truck Auto Truck Auto Truck 1 Reference L50 at 100 ft 2 Al DIstance 3 2 i- Element 4'3 Gradient U" ui - - - - 5 16 4/S Vertical Ln 6 Surface WS. 7 ' Shielding BarrIers 4 1...) 47 Structures & Plant. 8 TOTAL ADJUSTMENT I (add rows 2 through 7 o L50 AT OBSERVER (addrow1torow8 10 W.S L10 - L50 ADJUSTMENT

11 INTERRUPTED ADJUSTMENT I 12 - LiO AT OBSERVER < (add row 10 & 11 to row 9) L 10 13 15.6 ELEMENT TOTAL 10 14 WS,6 GRAND TOTAL L50 = dBA L10 = dBA

15 L10 - L = dBA

CRITERIA WORK SHEET

OBSERVER CATEGORY

TIME INTERVAL

i - Estimated Outside Traffic Level (dBA)

2 Ambient (dB) - - Lu 3 Outside Criterion (dBA)

C' - Ambient Difference (dB) (Subtract Line 3 from Line 1)

Criterion Difference Outside (dB) 5 (Subtract Line 3 from Line 1)

6 BuildIng Noise Reduction (dB)

7 ., Estimated Traffic Level Inside (dBA) O

8 - Inside Criterion (dBA)

9 Criterion Difference Inside (dB) (Subtract Line 8 from Line 7)

10 Compatabilily WORK SHEET NO. ROAD ELEMENT IDENTIFICATION Lane GrouDIna Chanae In Group DESCRIPTION Alinement Section Gradient Flow

Lane Group Element No. DESCRIPTION Position Parameters Pavement -- Type* D L 0 P N

121

* Element Type ClassificatIon: Type I InfInite Element II Semi-Infinite III Finite

WORK SHEET NO.2 TRAFFIC FLOW PARAMETERS

Line ROAD ELEMENT Symbol Ref. TIME INTERVAL

1 EstImated AADT, Vehicles per Day

2 Fig Cl Vehicle Volume, % AADT

3 V Vehicle Volume, vph

Fig C2 Truck/Auto Mix, % 411

5 1 Truck Volume, vph fr 1

6 ( Auto Volume, vph

Fig C3 Average Truck Speed, mph i

8 Fig C 3 Average Auto Speed, mph 61

WORKSHEET NO.3 ELEVATED AND DEPRESSED HIGHWAY ADJUSTMENT Un. I Number ROAD ELEMENT SI j Typo Ref. TIME INTERVAL

** ** 1 H1 Height of Elevated Freeway

2 PWS. Observer - Equivalent Lane DIst. U.'

3 DS " Observer - Shoulder Distance U.'

U.' TB5 B = H/(DE - D5) 6 H2 Depth of Depressed Freeway - >

7 DE RWS Observer - Equivalent Lane Dist.

8 D Observer - Cut Distance

9 A A=H/(DE-Dc)

08 B=H/DC t ELEVATED FREEWAY (a) Auto Fig B8 ADJUSTMENT I b) Trucks* DEPRESSED FREEWAY I Auto FlgB8 ADJUSTMENT Trucks* kL

Equivalent Hi** Lane ObsOlserver Height Observer Location H (a) Elevated Highway DS

Equivalent Observer Location Lane (b) Depressed Highway

D E 77~

* For trucks odd +5 dB to value given by Figure ** Height of elevated freeway above observer (H1) RIA

WORK SHEET NO. 4 SHIELDING ADJUSTMENT

— Line Number ROADWAY ELEMENT Symbol Ref. TIME INTERVAL 1 HI H.ight of Barrier 2 DB I Obs.rver — Barrier Distance Equivalent Lane - Barrier Distance 4 H2/1B 5 6 IFIg B9 Adjustment for Infinite Barrier 7 9 — Included Element Angle 8 a Included Barrier Angle cE 9 ! A=a/8 _--w U.' < 10 — Fj — Adjustment in dB 11 9 — 2 Comp. Barrier Angle 12 a — is Included Barrier Angle 13 A=a/90-8 E 14 Fig B9 u.i 01 Adjustment In dB 15 a Included Barrier Angle 16 A=a/180 ---O '0 17 FIg B9 < CLU djustment in dB

UJ Multiple Rows of Intervening Bidgs and Structures, Such As Houses, Apartments, 18 etc. Will Reduce Levels By Up To 10dB Assumed Adjustment in dB

A Design Value of 5 dB Noise Reduction 0 For Every IOQ ft of Planting (Depth) May Z Be Used if These Trees Are At Least 15 ft 19 TaIl and Sufficiently Dense So That No Visual Path Between Them and The Highway Exists Assumed Adjustment in dB

Total Adjustment for Structure 20 and Planting (Add Lines 18 and 19)

Equivalent Lane Location

RB DN DB \

. 0 — EP

Finite Roadway Element Semi Infinite Roadway Element 63

WORK SHEET NO. 5 110 ADJUSTMENT

un. Number ROAD ELEMENT Symbol Type TIME_INTERVAL R.f. VEHICLE TYPE Auto Truck Auto Truck Auto Truck Auto Truck

I V P.WS. Vehicle Volume, vph

2 S P.WS. Average Speed, mph PW.S. Observer - Equiv. Lone Distance, ft. EA Parameter A = VDE/, V.hlcI.s ft/rn Flg.B10 L10 Adjustment,. dB

WORK SHEET NO. 6 DECIBEL ADDITION

Sourceor

••_ - . ______•

List sound levels by source or Roadway Elements. Enter antilog table with right digit of sound level to obtain antilog value. Enter antilog on work sheet under antilog Columns. Position by entering left digit of antilog under the column numbered the same as the left digit of the sound level. Add the antilog values of the individual sources to obtain the antilog of the total sound level. Enter antilog table with antilog of total sound level. Obtain right digit of total sound level by selecting digit from table whose antilog Is closest numerically to the antilog obtained in Stop 4. Indentify column number containIng left most digit of the antilog derived from Stop 4. This is the numerical value of the left digit of the total sound level. 64

EXHIBIT B

FIGURES AND TABLES

DN (a) INFINITE ELEMENT

I Observer

SEMI- INFINITE ELEMENT (+) Observi (-)

Note: The Anglo 0 Can Be (i-) or (-) Depending If It Is Measured To The Right or Left

FINITE ELEMENT

1 Observer

Figure B-i. Definition of position parameters for roadway elements. 6000

65 4000

2000

c 000 800 U aC 600

1.7 41 400 C a -J Roadway Width C (No. of Lane I) 200 --1

100 80

10 100 1000 10,000 Observer - Near Lane Distance, DN - ft Figure B-2. Observer-equivalent lane distance as function of near lane distance and width of roadway.

BC II.APp.opeopoo- I P_.. go 14P0, 70 IIUIIIIIIIUI•IIIHHIlU!1M I a IHI

60 IIIIIIOhIUIIIPi!UiilILlP_ P-092111111 NIII uuuuIIIIIIp4øiiiiiuIuuIIIIIIuI.I u•iiuiriiiiiiiuuuuuiuiiuiui IIUiL01dIIIIIIHIIIIIIIIIIIlIIl UUIAiliIIIUIIIIIIIlIIIIIIIIIIIUIUl

KTC IuuIuIOIuuuIuHhIuuuIIIuIIuuIu UIlNhIIiIIIIIIIIHI•iNIIIiIiIIIUU

20 .IIuIuuIII.uIlIIuIIIuIIIuIIIIIuI.• cli ii:' Hourly Auto Volume, VA - vph Figure B-3. Plot of L0 for automobiles as a function of volume flow and average speed. 90

40 10 30 100 1000 10,000 Hourly Truck Volume, VT — vph Figure B-4. Plot of L. for trucks as is function of volume flow and average speed.

I II 11111 I I 1 I 1 liii! I 1 I

Roadway Width uiv No of Lanes

-20

-25

Observer — Near Lane Distance, DN-ft - Figure B-S. Distance adjustment to account for observer-near lane distance and width of roadway.

-15

-60 -40 -20 0 20 40 60 80 8 in degrees Figure B-6. Adjustment to account for semi-infinite element length.

-15

_20 1 I I I 0 20 40 60 80 100 120 140 160 8 in degrees Figure B-7. Adjustment to account for finite element length. 68

10 EME0111111MMEN111111MMEN I 1111111 151111111__I__I NiiI!!lEIIIIIl_I_I __•__ _ I I I

-20 EME0111111MEN011111100100 Ti Parameter A in ft Figure B-8. Adjustment for elevated and depressed roadway.

ADJUSTMENT FOR FINITE BARRIER IN dB

Infinite Parameter A I Barrier LPerformance 0 .1 .2 .3 .4 .5 .6. .7 .8 .9 I -5 R fl fl ..1 -1 -1 4 4 N-5 10 MENEM 1E==NHM=i III IIIlIIIIII_I_I

MENEM11111 "it __ EMENIF11__Iuii; tt.O2 u

-20 MENEM 1 0.1 1.0 . -H2 n i ft RB Figure B-9. Adjustment for roadside infinite barriers. 69 -IuuIuIIIIIIIuuIIuIuIuIIIuIIII IIIIIIIUhIIIIllhIIIIIIIIIIIUIIIIIIII iuuiiiiiiuiuiiiiiiuiiiiiiiuiuuiiiiii IIIHHhIIIIIIIIIIUIIIIIIIIIIEIUIIIIII iIlIIiiIUIIIIUhIIIIIIIIIIIUIIIIOHII IIIHIUNIIIIIIIIIIUIIIIIIIIIIIIllllhI IIIIIIIIAIIIIIIflhIIIflhIIlIIIIflHII Iuu'IH'Iu.'III'IIu'u"IIuu'II'IIII IuIIIIIIUII!uIIIIIIuuIIuIIuIuuuIIIII IIIIIIIIIIUIIiii!iIIIIIIIIIIIIIUIII UIIIIIIIUIIIHhIIIii!!!!!!!I!IIII

!111111!1111111111111111!111111111!.

Figure B-JO. Adjustment to L to obtain L10. b.4+k4es 4 +k o+ TABLE B-i TABLE B-2 ADJUSTMENT FOR INCREASED NOISE LEVEL CLASSIFICATION OF ROAD SURFACE AS IT RELATES OF TRUCKS ON GRADIENTS TO SURFACE INFLUENCE ON VEHICLE NOISE

ADJUST- ADJUST- GRADIENT MENT SURFACE MENT (%) (do) TYPE DESCRIPTION (cia) Smooth Very smooth, seal-coated 3to4 +2 asphalt pavement —5 5to6 +3 Normal Moderately rough asphalt and +5 concrete surface 0 Rough Rough aspalt pavement with The influence of gradients of 2% or less is considered to be negligible large voids ½ in. or larger in diameter, grooved concrete + 5

TABLE B-3 LEVEL ADJUSTMENT FOR INTERRUPTED FLOW

ADJUSTMENT (dB)

VEHJCLE TYPE L5o L10 Auto 0 +2 Truck 0 +4 70

TABLE B-4 EXAMPLE FOR DECIBEL ADDITION

ANTILOG TABLE RIGHT SOUND ANTILOG COLUMNS—LEFT DIGIT OF SOUND LEVEL DIGIT OF LEVEL ______SOUND SOURCE (dB) 9 8 7 6 5 4 3 2 LEVEL ANTILOG 1 65 3 1 6 2 0 1000 2 73 1 9 9 5 1 1259 3 69 7 9 4 4 2 1585 4 82 1 5 8 5 3 1995 5 56 3 9 8 1 4 2512 5 3162 6 3981 7 5013 8 6311 Total 83 1 8 9 9 5 4 1 9 7944

Comments on example: For 65 dB, enter antilog table with "5" to obtain the antilog "3162," etc. Enter "3162" on work sheet, with "3" in column 6, because the left digit of 65 dB sound level is "6." This is done for all the other listed sound levels. The columns in the example add to 1899541. Round off to four digits- 1900. From antilog table, 1900 is closest to 1995, the antilog of "3." The right digit of the total sound level is therefore "3." In the example, the left-most digit of the total sound level antilog is "1" and it appears in the column headed "8." The left digit of the total sound level is therefore "8," which with Step 5 determines the total sound level as "83." The total sound level of 65, 73, 69, 82, and 56 dB is thus 83 dB.

TABLE B-S RECOMMENDED DESIGN CRITERIA

L50 (dBA) L. (dBA) OBSERVER CATEGORY STRUCTURE DAY NIGHT DAY NIGHT 1 Residences Inside 45 40 51 46 2 Residences Outside ' 50 45 56 51 3 Schools Inside 40 40 46 46 4 Schools Outside 55 - 61 - 5 Churches Inside 35 35 41 41 6 Hospitals, Inside 40 35 46 41 7 convalescent homes Outside 50 45 56 51 8 Offices: Stenographic Inside 50 50 56 56 Private Inside 40 40 46 46 9 Theaters: Movies Inside 40 40 46 46 Legitimate Inside 30 30 36 36 10 Hotels, motels Inside 50 45 56 51

"Either inside or outside design criteria can be used, depending on the utility being evaluated.

TABLE B-6 DISTANCE ADJUSTMENT TO ACCOUNT FOR OBSERVER-NEAR LANE DISTANCE AND A 120-FT ROADWAY WIDTH

DISTANCE DISTANCE FROM OBSERVER DISTANCE FROM OBSERVER DISTANCE TO NEAR ADJUSTMENT TO NEAR ADJUSTMENT LANE (FT) (dB) LANE (FT) (dB) 50 0 600 —12 100 —2 700 —13 150 —5 800 —13 200 —7 900 —14 250 —8 1,000 —15 300 —9 1,200 —16 350 —10 1,400 —17 400 —10 1,600 —18 450 —11 1,800 —19 500 —11 2,000 —20 TABLE B-7 ELEVATED ROADWAY ADJUSTMENT FOR SHORT METHOD ONLY 71 ______ Roadway - DN Em.r. Lang Width -1 r 4 ______'1 ______// ' ,•/ Observer 1/ f/17/1/////////

Height of Distance from Observer to Near Lane (DN) Elevation Roadway I 00' 200' 300' 400' 600' 800' 1600'

H (feet) Adlustment in dB

5 - 5.0 - 1.0 0 0 0 0 0

10 -10.0 - 6.5 - 11.5 - 3.5 - 1.5 0.5 0

15 -12.0 - 9.0 - 7.0 - 5.5 - 3.5 - 2.0 - 0.5

20 -12.5 - 9.0 - 7.5 - 6.0 - 11.0 - 2.5 - 1.0

25 -13.5 -10.0 - 8.5 - 7.0 - 5.0 - 3.5 - 1.0

30 _14.5 -11.5 - 9.5 - 8.0 - 6.0 - 11.5 - 1.5

14Q -15.0 -13.5 -11.0 - 9.5 - 7.5 - 6.0 - 2.5

50 -15.0 -111.0 -12.0 -10.5 - 8.5 - 7.0 - 11.0

TABLE B-8 DEPRESSED ROADWAY ADJUSTMENT FOR SHORT METHOD ONLY DN Observer / 77777 4-Emer. Lane

pthOf Distance from Observer to Near Lane (DN) Depressed Roadway 100' 200' 300' 40' 600' 800' 1600'

H (feet) Adlustment in dB

0 0 0 0 0 0 0 0

5 - 6.0 - 5.5 - 5.0 - 5.0 - 5.0 - 5.0 - 5.0

10 -10.5 -10.5 -10.5 -10.5 -10.5 -10.5 -10.5

15 -13.0 -13.5 -13.5 -13.5 -13.5 -13.5 -13.5

20 -12.0 -111.0 -111.0 -111.0 -15.0 -15.0 -15.0

25 -11.0 -111.0 -15.0 -15.0 -15.0 -15.0 -15.0

30 -10.0 -111.5 -15.0 -15.0 -15.0 -15.0 -15.0

110 - 9.0 -111.5 -15.0 -15.0 -15.0 -15.0 -15.0

50 - -111.5 -15.0 -15.0 -15.0 -15.0 -15.0 WX

TABLE B-9 OUTSIDE-INSIDE NOISE REDUCTION

(dBA)

OBSERVER GEOGRAPHIC OPEN CLOSED CATEGORY STRUCTURE AREA WINDOWS WINDOWS 1 Residences South & southwest 12 20 North & northeast 17 25 3 Schools South & southwest 12 20 North & northeast 17 25 5 Churches All areas 20 30 6 Hospitals, convalescent All areas 17 25 homes S Offices All areas 17 25 9 Theaters All areas 20 30 10 Hotels, motels South & southwest 12 20 North & northeast 17 25

TABLE B-b IMPACT EVALUATION WHEN PREDICTED NOISE LEVELS EXCEED CRITERIA

PREDICTED NOISE LEVEL - CRITERION LEVEL IN dB

NO IMPACT SOME IMPACT GREAT IMPACT 1-1 LL~j F] 73

EXHIBIT C ILLUSTRATIVE DATA FROM "HIGHWAY CAPACITY MANUAL"

10 I

5 -c>0. —40

C 3

2 AM PM Hour of Day Figure C-i. Illustrative hourly volume variation with time 0 of day (derived from "Highway Capacity Manual," Figs. 12 4 8 12 4 8 12 3.6 and 3.7, relatIng to weekday traffic on rural and PM urban highways). Hour of Day Figure C-2. Illustrative truck/vehicle mix variation with time of day (derived from "Highway Capacity Manual," Fig. 3.3, relating to commercial vehicle activity on urban highway).

Avg. Highway Speed Zfl

rnp

mph --.-- 10 ------. - - - 0 400 800 1200 1 cn0 nnn Vehicle Volume per Lane, vph Figure C-3. Illustrative relationship between traffic volume per lane and average speed of vehicle travel for uninterrupted flow (derived from "High- way Capacity Manual," Fig. 3.41, for six-lane freeways and expressways. For different road configurations use appropriate data from this reference).

APPENDIX B

ILLUSTRATIVE RECORDING OF TRAFFIC NOISE

The following is a transcript of the text used in the "Illus- sociated with it also increases. In fact, traffic noise is one trative Recording of Traffic Noise," which is intended to of the most significant sources of noise in today's urban provide an illustrative accompaniment to the Design Guide. environment. The purposes of this recording are to discuss The dashed lines found throughout the text represent breaks acoustical concepts and terminology relevant to taking in the voice recording when the traffic noise samples are noise measurement to demonstrate how different vehicles presented. contribute to over-all traffic noise, to illustrate the extent Loan copies of the tape recording are available on request of noise reduction which can be achieved by different road- to the Program Director, NCHRP. way and building designs, and to introduce the listener to one of the most fundamental criteria of environmental acceptability. TEXT OF TAPE CALIBRATION INSTRUCTIONS Before we talk specifically about traffic noise, we should first define some acoustical terms. Our basic definition is This record must be played at a specific level if the sounds that of noise, which we define as unwanted sound. The on it are to be heard as intended for the purposes of this magnitude of noise is generally described in terms of its demonstration. The volume of your playback system must sound pressure. Because of the very great range of sound be adjusted so that the calibration noise which follows pressures usually encountered, a logarithmic scale is neces- registers a sound pressure level of 80 decibels on either the sary to provide a convenient system of units. This logarith- A or C scales of the standard sound level meter. The sound mic scale relates sound pressures to a common reference level meter must be placed at the intended listening position. level. A logarithmic unit of measurement is the decibel. If no sound measuring equipment is available, then the cor- The word decibel is often abbreviated to the letters d and rect playback level may be approximated by adjusting the B and referred to as dB. Sound pressures described in level of my speaking voice to a comfortable listening level. decibels are called sound pressure levels. A decibel scale This level should sound as though a person were speaking to may also be applied to other acoustic quantity such as you in a quiet environment, with normal vocal effort, at a sound power, hearing level, or wall transmission loss. distance of 3 feet. Calibration of the playback level without Sound pressure levels may also be defined in terms of fre- sound measuring equipment,. however, can yield only an quency weighting networks. Some weighted sound pressure' approximation of appropriate sound levels for the demon- levels are A-level, B-level, C-level, and D-level. Because stration noises. The calibration sound which you will hear the decibel scale is perfectly general it is necessary to specify next is an octave band of noise centered at 1,000 Hz. Adjust the scale associated with any particular decibel value. For the playback volume until the sound level reads 80 decibels example, in much of our following discussion we will refer on either the A or C scales. to traffic noises in terms of sound pressure levels measured with an A-weighting network and, therefore, reported in numerical values in units of dBA. TEXT OF ILLUSTRATIVE RECORDING Noise varies not only in magnitude but also in frequency How will the introduction of the new highway change the composition. The unit of measurement of frequency is the local noise environment? How acceptable will the new en- hertz or cycle per second. For example, the predominant vironment be to people living or working in the vicinity of exhaust frequencies of the diesel truck occur in the range the highway? What methods are available to the highway of 100 to 150 Hz. Middle C on the piano is 256 Hz. The engineer to remove or reduce adverse influences of highway high-frequency whine associated with the singing tire on noise? These questions have formed the basis of the study the concrete highway is in the range of 3,000 to 4,000 Hz. undertaken by the staff of Bolt Beranek and Newman, Inc., Now that we are familiar with the terminology which will for the Highway-Research-Board-administered National be employed, let's hear what some of these quantities and Cooperative Highway Research Program, sponsored by the numbers actually sound like. First, we will listen to a noise American Association of State Highway Officials in coop- which changes in magnitude but not in frequency content. eration with the Federal Highway Administration. This A bank of noise centered at 1,000 Hz will be presented at study has resulted in development of a Design Guide for several levels. The first level will be 70 decibels; that is to highway noise which provides the highway engineer with say, the sound pressure level in the band of noise is 70 the tools necessary to consider noise as a design parameter. decibels. This recording is presented as an illustrative accompaniment to the Design Guide. Next we will increase the magnitude of the sound by 1 decibel to 71 decibels. The sounds which we have just heard are easy to identify as traffic noise. As motor traffic increases, the noise as- 76

Now we will listen to both sounds together. First the 70 illustrated by the following sequence in which the same decibels and then the 71 decibels. car makes three passbys at .speeds in turn of 20, 40, and 60 miles per hour. Remember, we are still 100 feet from Clearly, a 1-decibel increase in magnitude is hardly dis- the roadway. cernible. Now we will play a series of sounds which will vary in The maximum levels reached on each of these events re- magnitude by 3, 5, and 10 decibels. Each time we will hear spectively were 50 dBA, 58 dBA, and 64 dBA. the 70-decibel sound followed by the one which is greater The noise of a truck is largely controlled at all speeds by than it. First, 70 decibels and 73 decibels. a combination of engine intake and exhaust noise and other noises generated by mechanical sources associated with the Now, 70 decibels and 75 decibels. power train. Since a truck driver tends to keep his engine speed relatively constant, truck noise shows on the average very little dependence upon road speed. This is illustrated Now, 70 decibels and 80 decibels. by the following sequence in which a truck makes two passes, one at 25 miles per hour, the other at 50 miles per Now let's listen to sounds of equal magnitude but different hour. frequency content. We will first repeat the band of noise which we just heard centered at 1,000 Hz. The sound pres- The maximum level of both events was about 76 dBA. A sure level of this band of noise is once again 70 decibels. truck is clearly much noisier than an automobile at any operating speed. Now compare it with a bank of noise of the same physical Now let us consider a number of automobiles on a magnitude centered at 250 Hz. hypothetical highway. Let us assume a four-lane configuration with narrow medians. Our point of observation is 100 feet from the nearest lane. A single automobile will pass by Finally, we will repeat the band of noise at 1,000 Hz and at a speed of 60 miles per hour. follow it with a band of noise of equal magnitude at 4,000 Hz. The noise signature here is clearly one which rises from a very low level to a peak and then falls once again. The Although each band of noise was presented with the same single most apt description of this event would be the value physical magnitude, we would not expect them to appear of the maximum level, in this case about 64 dBA. When the equally loud. This is because people in general perceive density of traffic flow on our highway increases, the char- sounds of different frequencies as of different magnitudes. acter of the noise signal changes. No longer is there a time We take these human differences in sensitivity to different when no vehicular noise is heard. The dynamic range of frequencies into account by employing different weighting the signal (that is, the level difference between the peaks scales such as those mentioned earlier. Of these scales, and the troughs) decreases progressively as traffic density A-weighted sound pressure levels provide a close correla- increases. Listen, for example, to the sound of the volume tion between the physical measurement and subjective as- flow of 600 automobiles per hour. On the average, one sessment of traffic noise. For this reason A-level has been vehicle passes our point of observation every 6 seconds. specified in international practice and is specified in many The average speed is 60 miles per hour. national standards for measurement of traffic noise. Yet another way in which noises may vary is in time. For example, here is a sound which varies by 20 decibels over Maintaining the same road speed but increasing the rate of a period of 10 seconds. Its magnitude will rise and fall flow to 2,000 automobiles per hour, an average of one symmetrically over this time interval. vehicle every two seconds, we would hear:

Now that we've become acquainted with a few of the con- The maximum stable flow that our hypothetical highway is cepts and terms of acoustical physics, let us consider the likely to sustain will be about 6,000 automobiles per hour. elements that are involved in traffic noise. There are two Still assuming an average speed of 60 miles per hour, this acoustically significant categories of vehicle which together would sound as follows: compose the bulk of traffic on our highways. These are automobiles and diesel trucks. Imagine yourself standing To demonstrate more clearly the effect of rate of flow on 100 feet from the near lane of a highway. An automobile traffic noise, let us repeat in quick succession that last is traveling along in this lane at a speed of 60 miles per sequence. First of all, the single automobile, then in flow hour. rates of, respectively, 600, 2,000, and 6,000 automobiles per hour. The single automobile: A major source of automobile noise, particularly at high speeds, derives from the interaction of the tire tread with A flow rate of 600 vehicles per hour: road surface. Tire noise increases markedly with speed, so automobile noise increases with speed also. This is 77

A flow rate of 2,000 vehicles per hour: the observer's distance from the roadway. Let us stand at a distance of 100 feet from our highway and listen in turn And a flow rate of 6,000 vehicles per hour: to the influence of elevating and depressing the highway a distance of 20 feet. In both cases we will take as our reference the 71-dBA level of the at-grade highway con- The increasing flow rate not only reduces the dynamic dition. First of all, at grade we hear: range of the noise, but also markedly increases the mean or the average level of the noise environment. Under the three conditions of 600, 2,000, and 6,000 automobiles per Then, with the highway elevated 20 feet: hour, average levels were 61 dBA, 66 dBA, and 71 dBA, respectively. Remember that the maximum level of the And, finally, with the highway depressed 20 feet we hear: single event was only 64 dBA. Thus, the levels of individual events are immersed in the average traffic noise environment at very modest flow rates. In these illustrations the elevated highway condition was Having synthesized the high-volume flow situation on our 11 decibels less noisy than the referenced grade-level high- highway, let us now introduce some trucks. The levels of way. The depressed highway was about 13 decibels quieter the truck maxima which you will hear are about 76 dBA. than the reference. We now have a very familiar traffic situation. The frequency spectrum of the traffic noise is also changed when shielding is introduced into the source- observer propagation path. Shielding is more effective at Having demonstrated the way in which single vehicles com- high frequencies than it is at low frequencies, so that the bine to form a total traffic noise situation, let us now exam- shielded highway sounds less "hissy" than an unshielded ine the different ways in which roadway and building grade-level road. This change in frequency accent should design can change the levels of traffic noise to which we are be quite clearly audible in these illustrative recordings. exposed. The traffic flow condition that we shall use Now let us move our observation location to 500 feet throughout the remainder of this recording is 6,000 auto- from the highway and listen again to the influence of elevat- mobiles per hour on a four-lane highway. The average ing and depressing the highway a distance of 20 feet. The vehicle speed is 60 miles per hour. With the highway at grade-level highway at this distance has an average noise grade level and our observation position 100 feet from the level of 62 dBA and sounds like this: nearest lane, we hear an average noise level of 71 dBA.

When we elevate the highway 20 feet we would expect to One means of noise control at our disposal is to increase hear: the distance between the roadway and our point of observation. For instance, if we change our position to one 200 feet distance from the roadway, we will hear: On the other hand, when the highway is depressed, we should hear: At 500 feet distance from the roadway we would hear: At this distance from the highway clearly the elevated con- We have just observed a level drop of about 4 decibels in figuration is relatively ineffective as a means of noise con- moving from 100 feet to 200 feet and a further drop of 5 trol. It is only about 3 decibels quieter than the grade-level decibels moving from 200 feet to 500 feet. Traffic noise situation. However, the performance of the depressed levels decrease with distance from the roadway at the rate highway at this distance is even better than it was at the of about 4 decibels for each doubling of distance. Thus, 100-foot distance. An attenuation of close to 15 decibels very significant changes in observer distances are required has been achieved. to produce a marked reduction in highway noise. Distance It must be stressed that the sounds and values of this alone, therefore, is not a very effective means of noise recording are intended to illustrate only the sorts of changes control. that can derive from various roadway designs. The actual So far we have assumed that the highway is located at noisiness of a design depends upon many parameters and grade level. Let us now consider the effect of changing the may vary widely as these parameters are changed. elevation of the highway with respect to the terrain on Roadside acoustic barriers provide a further means of which observers are located. When a highway is elevated shielding particular noise from the observer. To be effec- above grade or depressed below grade, a degree of shielding tive, an acoustic barrier must be impervious to sound, is introduced into the propagation path between the auto- sufficiently long to subtend a large angle of the observation mobile noise sources and the observer. The predominant position, and high enough to provide the required degree of sources of automobile noise we have already noted are attenuation. A 6-foot-high wall in our hypothetical highway located close to the roadway surface. The extent of acoustic situation should provide us with an attenuation of about 7 attenuation that results depends upon the geometry of the decibels at the 100-foot observation position. The wall, situation, upon such parameters as vertical displacement of however, would have to be in excess of 1,000 feet long. the pavement from the terrain, the width of the shoulder By increasing the height of the wall to 10 feet an attenuation between the pavement and the cut or fill slope line, and of about 10 decibels should be achieved. It is pertinent at 78 this point to comment on the shielding or other influences vironment at home where we derive most of our relaxation, of roadside planting. particularly in the evening and nighttime hours. The planting of ground cover on the cut- or ff1-slopes Let us try to illustrate the impact of traffic noise on our beside the highway has virtually no influence on the prop- ability to communicate by simulating various real-life situa- agated traffic noise. Similarly, trees or hedges planted tions. My voice level in this recording should be appearing along a highway have negligible influences on the amount of at your ear as though I were standing at a distance of 3 radiated sound unless the developed vegetation involved is feet from you talking at a normal voice level. Now let very wide. A design value of about 5 decibels per 100 feet me, figuratively speaking, move to a distance 10 feet away. width may be used. In general, the influence of vegetation As I talk from this far position with normal vocal effort on our response to traffic noise is psychological. the levels that you hear should be about 10 decibels below Many times we are more concerned with the noise en- the levels which you have been hearing so far. The gain of vironment inside a house than we are with the noise envir- the system through which this record is being played has onment outside a house. Let us compare the level of traffic been calibrated to your ability to hear me clearly from this noise that we hear outside and inside a typical residential distance. It is some measure of the adequacy of this room structure located 100 feet from the hypothetical highway. for this sort of conversation. Outside the house we hear: Having demonstrated the influence of speaker-listener distances of voice levels, let us now examine the effects of different simulated traffic environments on voice intelligi- While inside with the windows open we hear: bility. We will superimpose the simulated traffic environment on my normal speaking voice at the two speaking distances of 3 feet and 10 feet. I will speak the introductory Clearly, there is significant benefit to be gained by retreat- sentences of this recording during the traffic noises. ing indoors—a benefit amounting to 14 decibels or so. Still Throughout these tests we assume the usual traffic situation further improvement is gained if we close the house win- of 6,000 vehicles per hour at a speed of 60 miles per hour. dows. First of all, with the windows open: Judge for yourself the acceptability of the speaking environment in each of the following cases. First, let us stand Next, with the windows closed: outside 100 feet from the roadway. Using a speaker-listener distance of 3 feet you would hear this

Finally, to complete the comparison let us go back outside. Under this condition the degree of speech intelligibility is very poor. Few, if any, words are understood. At a Whereas the noise reduction achieved was about 14 decibels speaking distance of 10 feet I would be virtually inaudible. with the open windows, the closed windows situation pro- If we move inside a house and leave the windows open, the vides a final environment some 25 decibels below the out- conversation at 3 feet would then sound like this: side traffic levels. The final environment achieved in our house was therefore about 46 dBA. It should be noted that This condition is significantly more intelligible than before, the actual noise reduction provided by a building depends but, nevertheless, hardly satisfactory. When the speaking strongly upon the details of its structure. The examples distance is increased to 10 feet, the intelligibility again demonstrated here, however, are representative. becomes very poor: Now that we have learned something about the way roadway and building design can reduce highway noise, let us very briefly consider the final link in the chain—the If now the highway is depressed or elevated the distance of matter of environmental acceptability. There are many 20 feet above or below the terrain, a further 12 decibels factors involved in the way in which individuals react to the or so of attenuation may be obtained. Conversation within noise environment. Some of these are purely subjective, the house would then sound like this at a distance of 3 feet: related to fear or distaste that we might have for the noise, of course. Other factors relate to the behavioral aspects of At a distance of 10 feet the conversation would sound like the noise environment and involve interference with on- this: going activities such as speech, sleep, learning, and so forth. A third grouping of factors is physiological, relating to While by no means ideal, the environment is now approach- factors such as hearing loss or pain. Experimental studies ing acceptability from the viewpoint of speech intelligibility. have shown that one of the most important factors in deter- Further improvement to the extent of about 12 decibels can mining acceptance of a noise environment is the ease with be achieved by closing the windows. At a 10-foot speaking which we can communicate in the environment. Communi- position we would hear: cation requirements tend to vary with location and occupa- tion. On a downtown street, for example, we fully expect to communicate over small distances only and, if necessary, Hopefully, these tests have demonstrated to you some in- to raise our voices. In the office we may wish to hold con- fluences of traffic noise on the communication environment. ferences over distances of 10 to 15 feet at normal voice As a final test and as an apt conclusion to this illustrative level. We are especially critical of the communication en- recording, we will allow you to experiment with one of the 79 environments which we have just simulated. The condition that you will hear relates to at-grade highway at a distance of 100 feet as heard from inside a house with open win- This is the end of the illustrative recording. We hope that dows. Test with a colleague the adequacy of this environ- it helps you develop an appreciation for some of the ment for different speech levels and distances. parameters of traffic noise. Published reports of the Rep. No. Title NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM 20 Economic Study of Roadway Lighting (Proj. 5-4), are available from: 77 p., $3.20 21 Highway Research Board Detecting Variations in Load-Carrying Capacity of National Academy of Sciences Flexible Pavements (Proj. 1-5), 30 p., $1.40 22 2101 Constitution Avenue Factors Influencing Flexible Pavement Performance Washington, D.C. 20418 (Proj. 1-3(2)), 69 p., $2.60 23 Methods for Reducing Corrosion of Reinforcing Steel (Proj. 6-4), 22 p., $1.40 Rep. 24 Urban Travel Patterns for Airports, Shopping Cen- No. Title ters, and Industrial Plants (Proj. 7-1), 116 p., -* A Critical Review of Literature Treating Methods of $5.20 Identifying Aggregates Subject to Destructive Volume 25 Potential Uses of Sonic and Ultrasonic Devices in Change When Frozen in Concrete and a Proposed Highway Construction (Proj. 10-7), 48 p., $2.00 Program of Research—Intermediate Report (Proj. 26 Development of Uniform Procedures for Establishing 4-3(2)), 81 p., $1.80 Construction Equipment Rental Rates (Proj. 13-1), 1 Evaluation of Methods of Replacement of Deterio- 33 p., $1.60 rated Concrete in Structures (Proj. 6-8), 56 p., 27 Physical Factors Influencing Resistance of Concrete $2.80 to Deicing Agents (Proj. 6-5), 41 p., $2.00 2 An Introduction to Guidelines for Satellite Studies of 28 Surveillance Methods and Ways and Means of Com- Pavement Performance (Proj. 1-1), 19 p., $1.80 municating with Drivers (Proj. 3-2), 66 p., $2.60 2A Guidelines for Satellite Studies of Pavement Per- 29 Digital-Computer-Controlled Traffic Signal System formance, 85 p.+9 figs., 26 tables, 4 app;, $3.00 for a Small City (Proj. 3-2), 82 p., $4.00 3 Improved Criteria for Traffic Signals at Individual 30 Extension of AASHO Road Test Performance Con- Intersections—Interim Report (Proj. 3-5), 36 p., cepts (Proj. 1-4(2)), 33 p., $1.60 $1.60 31 A Review of Transportation Aspects of Land-Use 4 Non-Chemical Methods of Snow and Ice Control on Control (Proj. 8-5), 41 p., $2.00 Highway Structures (Proj. 6-2), 74 p., $3.20 32 Improved Criteria for Traffic Signals at Individual 5 Effects of Different Methods of Stockpiling Aggre- Intersections (Proj. 3-5), 134 p., $5.00 gates—Interim Report (Proj. 10-3), 48 p., $2.00 33 Values of Time Savings of Commercial Vehicles 6 Means of Locating and Communicating with Dis- (Proj. 2-4), 74 p., $3.60 abled Vehicles—Interim Report (Proj. 3-4), 56 p. 34 Evaluation of Construction Control Procedures— $3.20 Interim Report (Proj. 10-2), 117 p., $5.00 7 Comparison of Different Methods of Measuring 35 Prediction of Flexible Pavement Deflections from Pavement Condition—Interim Report (Proj. 1-2), Laboratory Repeated-Load Tests (Proj. 1-3(3)), 29p., $1.80 117p., $5.00 8 Synthetic Aggregates for Highway Construction 36 Highway Guardrails—A Review of Current Practice (Proj. 4-4), 13 p., $1.00 (Proj. 15-1), 33 p., $1.60 9 Traffic Surveillance and Means of Communicating 37 Tentative Skid-Resistance Requirements for Main with Drivers—Interim Report (Proj. 3-2), 28 p., Rural Highways (Proj. 1-7), 80 p., $3.60 $1.60 38 Evaluation of Pavement Joint and Crack Sealing Ma- 10 Theoretical Analysis of Structural Behavior of Road terials and Practices (Proj. 9-3), 40 p., $2.00 Test Flexible Pavements (Proj. 1-4), 31 p., $2.80 39 Factors Involved in the Design of Asphaltic Pave- 11 Effect of Control Devices on Traffic Operations— ment Surfaces (Proj. 1-8), 112 p., $5.00 Interim Report (Proj. 3-6), 107 p., $5.80 40 Means of Locating Disabled or Stopped Vehicles 12 Identification of Aggregates Causing Poor Concrete (Proj. 3-4(1)), 40 p., $2.00 Performance When Frozen—Interim Report (Proj. 41 Effect of Control Devices on Traffic Operations 4-3(1)), 47p., $3.00 (Proj. 3-6), 83 p., $3.60 13 Running Cost of Motor Vehicles as Affected by High- 42 Interstate Highway Maintenance Requirements and way Design—Interim Report (Proj. 2-5), 43 p., Unit Maintenance Expenditure Index (Proj. 14-1), $2.80 144 p., $5.60 14 Density and Moisture Content Measurements by 43 Density and Moisture Content Measurements by Nuclear Methods—Interim Report (Proj. 105), Nuclear Methods (Proj. 10-5), $2.00 $3.00 38 p., 32 p., 44 Traffic Attraction of Rural Outdoor Recreational 15 Identification of Concrete Aggregates Exhibiting Areas (Proj. 7-2), Frost Susceptibility—Interim Report (Proj. 4-3(2)), 28 p., $1.40 45 Development of Improved Pavement Marking Ma- 66 p., $4.00 16 Protective Coatings to Prevent Deterioration of Con- terials—Laboratory Phase (Proj. 5-5), 24 p., $1.40 crete by Deicing Chemicals (Proj. 6-3), 21 p., $1.60 46 Effects of Different Methods of Stockpiling and 17 Development of Guidelines for Practical and Realis- Handling Aggregates (Proj. 10-3), 102 p., $4.60 tic Construction Specifications (Proj. 10-1); 109 p., $6.00 47 Accident Rates as Related to Design Elements of 18 Community Consequences of Highway Improvement Rural Highways (Proj. 2-3), 173 p., $6.40 (Proj. 2-2), 37 p., $2.80 48 Factors and Trends in Trip Lengths (Proj. 7-4), 19 Economical and Effective Deicing Agents for Use on 70 p., $3.20 Highway Structures (Proj. 6-1), 19 p., $1.20 49 National Survey of Transportation Attitudes and Behavior—Phase I Summary Report (Proj. 20-4), * Highway Research Board Special Report 80. 71. p., $3.20 Rep. Rep. No. Title No. Title 50 Factors Influencing Safety at Highway-Rail Grade 76 Detecting Seasonal Changes in Load-Carrying Ca- Crossings (Proj. 3-8), 113 p., $5.20 pabilities of Flexible Pavements (Proj. 1-5(2)), 51 Sensing and Communication Between Vehicles (Proj. 37 p., $2.00 3-3), 105 p., $5.00 77 Development of Design Criteria for Safer Luminaire 52 Measurement of Pavement Thickness by Rapid and Supports (Proj. 15-6), 82 p., $3.80 Nondestructive Methods (Proj. 10-6), 82 p., 78 Highway Noise ---Measurement, Simulation, and $3.80 Mixed Reactions (Proj. 3-7), 78 p., $3.20 53 Multiple Use of Lands Within Highway Rights-of- 79 Development of Improved Methods for Reduction of Way (Proj. 7-6), 68 p., $3.20 Traffic Accidents (Proj. 17-1), 163 p., $6.40 54 Location, Selection, and Maintenance of Highway 80 Oversize-Overweight Permit Operation on State High- Guardrails and Median Barriers (Proj. 15-1(2)), ways (Proj. 2-10), 120 p., $5.20 63 p., $2.60 81 Moving Behavior and Residential Choice—A Na- 55 Research Needs in Highway Transportation (Proj. tional Survey (Proj. 8-6), 129 p., $5.60 20-2), 66 p., $2.80 82 National Survey of Transportation Attitudes and 56 Scenic Easements—Legal, Administrative, and Valua- Behavior—Phase II Analysis Report (Proj. 20-4), tion Problems and Procedures (Proj. 11-3), 174 p., 89 p., $4.00 $6.40 83 Distribution of Wheel Loads on Highway Bridges 57 Factors Influencing Modal Trip Assignment (Proj. (Proj. 12-2), 56 p., $2.80 8-2), 78 p., $3.20 84 Analysis and Projection of Research on Traffic 58 Comparative Analysis of Traffic Assignment Tech- Surveillance, Communication, and Control (Proj. niques with Actual Highway Use (Proj. 7-5), 85 p., 3-9), 48 p., $2.40 $3.60 85 Development of Formed-in-Place Wet Reflective 59 Standard Measurements for Satellite Road Test Pro- Markers (Proj. 5-5), 28 p., $1.80 gram (Proj. 1-6), 78 p., $3.20 86 Tentative Service Requirements for Bridge Rail Sys- 60 Effects of Illumination on Operating Characteristics tems (Proj. 12-8), 62 p., $3.20 of Freeways (Proj. 5-2) 148 p., $6.00 87 Rules of Discovery and Disclosure in Highway Con- 61 Evaluation of Studded Tires—Performance Data and demnation Proceedings (Proj. 11-1(5)), 28 p., Pavement Wear Measurement (Proj. 1-9), 66 p., $2.00 $3.00 88 Recognition of Benefits to Remainder Property in 62 Urban Travel Patterns for Hospitals, Universities, Highway Valuation Cases (Proj. 11-1(2)), 24 p., $2.00 Office Buildings, and Capitols (Proj. 7-1), 144 p., $5.60 89 Factors, Trends, and Guidelines Related to Trip 63 Economics of Design Standards for Low-Volume Length (Proj. 7-4), 59 p., $3.20 90 Rural Roads (Proj. 2-6), 93 p., $4.00 Protection of Steel in Prestressed Concrete Bridges 64 Motorists' Needs and Services on Interstate Highways (Proj. 12-5), 86 p., $4.00 91 (Proj. 7-7), 88 p., $3.60 Effects of Deicing Salts on Water Quality and Biota 65 One-Cycle Slow-Freeze Test for Evaluating Aggre- —Literature Review and Recommended Research gate Performance in Frozen Concrete (Proj. 4-3(1)), (Proj. 16-1), 70 p., $3.20 92 21 p., $1.40 Valuation and Condemnation of Special Purpose 66 Identification of Frost-Susceptible Particles in Con- Properties (Proj. 11-1(6)), 47 p., $2.60 93 crete Aggregates (Proj. 4-3(2)), 62 p., $2.80 Guidelines for Medial and Marginal Access Control 67 Relation of Asphalt Rheological Properties to Pave- on Major Roadways (Proj. 3-13), 147 p., ment Durability (Proj. 9-1), 45 p., $2.20 $6.20 68 Application of Vehicle Operating Characteristics to 94 Valuation and Condemnation Problems Involving Geometric Design and Traffic Operations (Proj. 3 Trade Fixtures (Proj. 11-1(9)), 22 p., $1.80 10), 38 p., $2.00 95 Highway Fog (Proj. 5-6), 48 p., $2.40 69 Evaluation of Construction Control Procedures— 96 Strategies for the Evaluation of Alternative Trans- Aggregate Gradation Variations and Effects (Proj. portation Plans (Proj. 8-4), 111 p., $5.40 10-2A), 58 p., $2.80 97 Analysis of Structural Behavior of AASHO Road 70 Social and Economic Factors Affecting Intercity Test Rigid Pavements (Proj. 1-4(1)A), 35 p., Travel (Proj. 8-1), 68 p., $3.00 $2.60 71 Analytical Study of Weighing Methods for Highway 98 Tests for Evaluating Degradation of Base Course Vehicles in Motion (Proj. 7-3), 63 p., $2.80 Aggregates (Proj. 4-2), 98 p. $5.00 72 Theory and Practice in Inverse Condemnation for 99 Visual Requirements in Night Driving (Proj. 5-3), Five Representative States (Proj. 11-2), 44 p., 38 p., $2.60 $2.20 100 Research Needs Relating to Performance of Aggre- 73 Improved Criteria for Traffic Signal Systems on gates in Highway Construction (Proj. 4-8), 68 p., Urban Arterials (Proj. 3-5/1), 55 p., $2.80 $3.40 74 Protective Coatings for Highway Structural Steel 101 Effect of Stress on Freeze-Thaw Durability of Con- (Proj. 4-6), 64 p., $2.80 crete Bridge Decks (Proj. 6-9), 70 p., $3.60 74A Protective Coatings for Highway Structural Steel— 102 Effect of Weldments on the Fatigue Strength of Steel Literature Survey (Proj. 4-6), 275 p., $8.00 Beams (Proj. 12-7), 114 p., $5.40 74B Protective Coatings for Highway Structural Steel— 103 Rapid Test Methods for Field Control of Highway Current Highway Practices (Proj. 4-6), 102 p., Construction (Proj. 10-4), 89 p., $5.00 $4.00 104 Rules of Compensability and Valuation Evidence 75 Effect of Highway Landscape Development on for Highway Land Acquisition (Proj. 11-1), Nearby Property (Proj. 2-9), 82 p., $3.60 77 p., $4.40 Rep. No. Title 105 Dynamic Pavement Loads of Heavy Highway Vehi- cles (Proj. 15-5), 94 p., $5.00 106 Revibration of Retarded Concrete for Continuous Bridge Decks (Proj. 18-1), 67 p., $3.40 107 New Approaches to Compensation for Residential Takings (Proj. 11-1(10)), 27 p., $2.40 108 Tentative Design Procedure for Riprap-Lined Chan- nels (Proj. 15-2), 75 p., $4.00 109 Elastomeric Bearing Research (Proj. 12-9), 53 p., $3.00 110 Optimizing Street Operations Through Traffic Regu- lations and Control (Proj. 3-11), lOOp., $4.40 111 Running Costs of Motor Vehicles as Affected by Road Design and Traffic (Proj. 2-5A and 2-7), 97 p., $5.20 112 Junkyard Valuation—Salvage Industry Appraisal Principles Applicable to Highway Beautification (Proj. 11-3(2)), 41 p., $2.60 113 Optimizing Flow on Existing Street Networks (Proj. 3-14), 414 p., $15.60 114 Effects of Proposed Highway Improvements on Prop- erty Values (Proj. 11-1(1)), 42 p., $2.60 115 Guardrail Performance and Design (Proj. 15-1 (2)), 70 p., $3.60 116 Structural Analysis and Design of Pipe Culverts (Proj. 15-3), 155 p., $6.40 117 Highway Noise—A Design Guide for Highway En- gineers (Proj. 3-7), 79 p., $4.60

Synthesis of Highway Practice 1 Traffic Control for Freeway Maintenance (Proj. 20-5, Topic 1), 47 p., $2.20 2 Bridge Approach Design and Construction Practices (Proj. 20-5, Topic 2), 30 p., $2.00 3 Traffic-Safe and Hydraulically Efficient Drainage Practice (Proj. 20-5, Topic 4), 38 p., $2.20 4 Concrete Bridge Deck Durability (Proj. 20-5, Topic 3), 28 p., $2.20 5 Scour at Bridge Waterways (Proj. 20-5, Topic 5), 37 p., $2.40 6 Principles of Project Scheduling and Monitoring (Proj. 20-5, Topic 6), 43 p., $2.40 T H E NATIONAL ACADEMY OF SCIENCES is a private, honorary organization of more than 700 scientists and engineers elected on the basis of outstanding contributions to knowledge. Established by a Congressional Act of Incorporation signed by President Abraham Lincoln on March 3, 1863, and supported by private and public funds, the Academy works to further science and its use for the general welfare by bringing together the most qualified individuals to deal with scientific and technological problems of broad significance. Under the terms of its Congressional charter, the Academy is also called upon to act as an official—yet independent—adviser to the Federal Government in any matter of science and technology. This provision accounts for the close ties that have always existed between the Academy and the Government, although the Academy is not a governmental agency and its activities are not limited to those on behalf of the Government.

THE NATIONAL ACADEMY OF ENGINEERING was established on December 5, 1964. On that date the Council of the National Academy of Sciences, under the authority of its Act of Incorporation, adopted Articles of Organization bringing the National Academy of Engineering into being, independent and autonomous in its organization and the election of its members, and closely coordinated with the National Academy of Sciences in its advisory activities. The two Academies join in the furtherance of science and engineering and share the responsibility of advising the Federal Government, upon request, on any subject of science or technology.

THE NATIONAL RESEARCH COUNCIL was organized as an agency of the National Academy of Sciences in 1916, at the request of President Wilson, to enable the broad community of U. S. scientists and engineers to associate their efforts with the limited membership of the Academy in service to science and the nation. Its members, who receive their appointments from the President of the National Academy of Sciences, are drawn from academic, industrial and government organizations throughout the country. The National Research Council serves both Academies in the discharge of their responsibilities. Supported by private and public contributions, grants, and contracts, and volun- tary contributions of time and effort by several thousand of the nation's leading scientists and engineers, the Academies and their Research Council thus work to serve the national interest, to foster the sound development of science and engineering, and to promote their effective application for the benefit of society.

THE DIVISION OF ENGINEERING is one of the eight major Divisions into which the National Research Council is organized for the conduct of its work. Its membership includes representatives of the nation's leading technical societies as well as a number of members-at-large. Its Chairman is appointed by the Council of the Academy of Sciences upon nomination by the Council of the Academy of Engineering.

THE HIGHWAY RESEARCH BOARD, organized November 11, 1920, as an agency of the Division of Engineering, is a cooperative organization of the highway technologists of America operating under the auspices of the National Research Council and with the support of the several highway departments, the Federal Highway Administration, and many other organizations interested in the development of transportation. The purpose of the Board is to advance knowledge concerning the nature and performance of transportation systems, through the stimulation of research and dissemination of information derived therefrom. HIGHWAY RESEARCH BOARD NON-PROFIT ORG. NATIONAL ACADEMY OF SCIENCES—NATIONAL RESEARCH COUNCIL 2101 Constitution Avenue Washington, D. C. 20418 U.S. POSTAGE PAID WASHINGTON, D.C. PERMIT NO. 42970 ADDRESS CORRECTION REQUESTED