TR News 240: Addressing Noise from the U.S. Transportation System

Home , Roadway noise

SYSTEMS U.S.TRANSPORTATION ADDRESSING THE NOISEFROM 4 TR NEWS 240 SEPTEMBER–OCTOBER 2005 walls andlandscaping from thenoisebybarrier neighborhoods protected through residential Washington, D.C., pass Interstate 66insuburban automobile traffic on Metrorail and Massachusetts. Burlington, Miller &Hanson, President, Harris Miller The authorisSeniorVice NICHOLAS P. MILLER Measures andCountermeasures . T enough andfrequent enough,however, thesounds being isasubjectofcontinuingdebate.Whenloud common transportation sources are showninTable 1; Estimates ofthemaximumsoundlevelsproduced by Transportation SoundLevels diminish thequalityoflife(seebox,page6). sounds are tohumanhealthandwell- sounds outdoors.Howdetrimentalthese economy, are thepredominant source of ransportation systems,vitaltotheU.S. the terrain,locationofbuildingsorothershield- factors thataffect thepropagation ofsound—suchas levels atotherdistancesrequires informationabout can bemeasured reliably. Thederivationofsound feet—the distancesatwhichthesource soundlevels feet, andtheground transportation sources are for50 ciated withspecificdistancesandoperatingconditions. distance from thesource; thelevelsinTable 1are asso- be associatedwithalocationontheground orwitha sourceswaterway Sound levelsshould are notincluded.

The aircraft soundlevelsare fordistancesof1,000

, WMATA , L L : P EVINE ARRY HOTO ing structures, the meteorological conditions, the air- TABLE 1 Approximate Maximum Sound Levels for Transportation Sources craft engine mounting, the aircraft elevation, and the direction of flight in relation to the listener. The max- Approximate imum levels at a distance of 50 feet would be at least Maximum 25 decibels (dB) lower if heard at 1,000 feet. Estimated Speed/ A-Weighted Sound Distance, The levels for the surface transportation sources are Source Type Operating Condition Level, dB(A) feet from federal agency models. The aircraft levels derive Aircraft from the Federal Aviation Administration’s (FAA’s) Commercial jet Takeoff 85 1,000 aircraft noise model data and from field measure- Commercial jet High Altitude Cruise 85 1,000 ments. The sound levels should be considered typical Corporate jet Takeoff 85 1,000 or average; actual levels will vary above and below Propeller aircraft Takeoff 70–80 1,000 those indicated in the table. Helicopter Cruise 70 1,000 No Escape Roadway Vehicles Heavy truck 50 mph 83 50 Stand outside almost anywhere in the continental United States, and within a short time—probably Medium truck 50 mph 79 50 less than 1 hour—the sound of a truck, automobile, Automobile 50 mph 72 50 airplane, or train will be audible. The percentage of Rail Vehicles land in each county in which the various transporta- Diesel locomotive 50 mph 88 50 tion sources are likely to be heard during the daytime Rail cars 50 mph 80 50 can be estimated from standard transportation sound Locomotive horns - 96–110 50 levels, the routes followed by each mode, and esti- dB(A) = A-weighted decibels, a summation of sound levels across frequencies. mates of the background sound levels throughout the continental United States. Figures 1, 2, and 3 show the percentages of land Aircraft Sound Metric in each county in which the sounds of roadway FAA has identified a day–night average sound level traffic, rail traffic, and high-altitude jets may be (DNL) of 65 dB from aircraft operations as the limit heard (1). of acceptability for residential housing (see Figure A, The roadway results represent the network of page 6). Federal funding is available to assist with limited access, primary, and secondary roads; local sound insulation and property acquisition in areas roads are not included. The rail results are for with noise above the acceptable level. The federal freight lines only, and the aircraft results are for government, however, does not set land use policies; high-altitude intercity jet traffic only—general avi- local authorities determine the relationship between ation operations or departures and arrivals in the land use and sound levels. FIGURE 1 Percentages of vicinity of airports are not included. The road and DNL is a measure of total sound energy in 24 county areas in which the jet results, therefore, are likely to be underestimates, hours and therefore may include many combina- sounds of road traffic are particularly for densely populated areas and for the tions of aircraft sound levels and events. Three noticeable during the day. vicinity of major airports.

Aircraft Noise Aircraft noise is an issue for people who live near airports. Noise is the reason most often cited for public resistance to increases in runway capacity or to alter- TR NEWS 240 SEPTEMBER–OCTOBER 2005 ations in the use of airspace. Aircraft-produced sound can reach levels that interfere with speech outdoors in communities some distance from an airport. For example, a modern commercial jet can produce sound levels of 70 dB(A)1 to 80 dB(A) up to 3 miles from a runway, loud enough to interfere with speech outdoors for about 20 to 35 seconds. A moderately busy commercial airport with 200 to 300 daily departures could interfere with speech 10 to 20 times per hour.

1 dB(A) = A-weighted decibels. See box, page 6. 5 example combinations of sound levels and operations that would produce a DNL of approximately 65 dB—assuming that all operations occur between 7 a.m. and 10 p.m.—are shown in Table 2 (page 9). Levels that exceed 60 dB(A) would begin to interfere with normal conversations outdoors.

Aircraft Noise Issues Because commercial jet aircraft departures and arrivals are the primary sources of noise exposure in the vicinity of airports, any proposal that may increase the number of flights or alter the neighborhoods over which the aircraft fly is likely to arouse public concern. Lengthening runways, building runways, or adding gates—any plan that could be per- ceived to increase the sound exposure from aircraft—can generate public resistance. FIGURE 2 Percentages of county areas in which the sounds of rail traffic are Around airports with no scheduled commercial noticeable during the day. operations, loud jet or loud propeller operations are a

Introduction to Sound Metrics and Criteria

ound is quantified either as a total accumulation of sound Senergy for a period of time or as a measure of a single event. Almost all environmental sound is measured in A-weighted decibels [dB(A) or dBA]. A-weighting is a summation of the sound levels across frequencies; this summation de-emphasizes the levels at different frequencies and corresponds to the way people hear. The total accumulation metrics are called equivalent levels and

represent the sound levels for either 1 hour, symbolized as LAeq,H,

Leq(H), or Leq—if the time period is defined—or a 24-hour period,

FIGURE B A 24-hour measurement.

called the day-night average sound level (DNL or Ldn). DNL includes a weighting or penalty of 10 dB for sound that occurs between 10 p.m. and 7 a.m. Single events are quantified as an accumulation of sound energy over the duration of the event, termed the sound exposure

level (SEL); or as a maximum level, Lmax; or as the length of time that the sound was above a specified threshold, known as time above (TA). According to the U.S. Environmental Protection Agency (EPA), cumulative sound exposure below 55 dB DNL poses minimal risk of adverse effects on human health, as well as minimal annoyance. Figure A shows typical values of DNL for various locations and identifies the levels established by EPA, the Department of Hous-

TR NEWS 240 SEPTEMBER–OCTOBER 2005 TR NEWS 240 SEPTEMBER–OCTOBER ing and Urban Development, and the Federal Aviation Adminis- 6 FIGURE A Typical values of DNL. tration in making decisions about funding assistance. TR NEWS 240 SEPTEMBER–OCTOBER 2005 7 compares several typical max- D charts the sound level of a single event, showing the charts the sound level of a single event, C Figure in a single event, the As the summation of all the sound energy

FIGURE D Typical maximum sound levels. maximum FIGURE D Typical maximum level and the TA. Figure maximum level and the TA. imum sound levels. the maximum. The SEL SEL is generally 5 to 10 dB higher than a more complete reflects the duration of a sound and provides of an event. estimate of the disruptive or annoying quality

: E : P L RIKA HOTO LOYD shows the measured levels at one site, B Helicopters are not usually louder than other air- not usually louder than other Helicopters are of sound include sources Other aviation-related The federal agencies responsible for managing transportation Hourly equivalent levels contribute to the value of DNL for the FIGURE C Single-event time history. craft (see Table 1) but can be identified easily by 1) but craft (see Table “blade slap” occurs, and can sound, especially when also travel slower than cause complaints. Helicopters for a longer time. and can be heard fixed-wing aircraft aux- a flight; or before engine testing for maintenance electricity while the iliary power units that provide and the low-fre- is at a gate; taxiing aircraft; aircraft is This last source at takeoff. jets quency rumble from because the A-weighted and control to assess difficult low-frequency sound level does not represent source of noise exposure and, if frequent or at night, a or at night, if frequent and, of noise exposure source a loud corporate jets of complaints. A few likely cause concern, regardless can raise public week, for example, jet operations, with no loud In areas of DNL values. flying over quiet neigh- aircraft the sound of propeller week- on enough—particularly if frequent borhoods, ends—may raise concern. noise have established criteria, standards, or guidelines to identify when an impact occurs and when an increase in sound is substantial. If a study indicates that a federally funded project would produce an impact or a substantial increase in sound level, specific actions are required, including a detailed analysis and an examination of ways to reduce the noise. Under certain conditions, federal funds are available for noise reduction. The reductions must meet minimum goals, and the methods or actions must be tech- nically and economically feasible. 24-hour period; Figure indicating little variation from hour to hour, except in the middle indicating little variation from hour to hour, of the night. L(01), L(33), and L(90) are the levels exceeded 1 per- and 90 percent of the hour, 33 percent of the cent of the hour, respectively. hour, 8 TR NEWS 240 SEPTEMBER–OCTOBER 2005 E peller designs,butthedecreaseislimited. namic modelingtechniqueshavedevelopedlower-noise pro- the thrustforflightiswhatcausesnoise.Advancedaerody- down. propeller spinsfaster, thepitchgoesup;ifslower, thepitchgoes the noiseisdirectlyrelatedtospeedofpropeller. Ifthe the propellersslicingthroughair. Thepitchorfrequencyof to createproblemsfortheneighborhoodsaroundairports. portion oftheengine’s powerradiatesasnoisebutissufficient frame. Enginenoiseiswastedorlostenergy. Onlyaminute main sources:thepropeller-driven orjetenginesandtheair- less familiar. these noises,however, are the runway. Thecausesof an airplaneapproaching or thewhistlingwhooshof rumble ofajettakingoff In contrast,jetengineshavetwomajornoise-producing Reducing propellernoiseisalmostimpossible—producing The noisegeneratedbyapropellerisbuzzing,caused Aircraft noisehastwo aircraft noise—thedeep veryone isfamiliarwith Propeller Buzz,JetRoar, andAirframeNoise Causes andControls

JOSEPH CZECH

L W : P ABORATORIES YLE HOTOS remains anecessity. 0.5 million.Nevertheless,reducing aircraftnoiseemissions aircraft noisehasdecreased from approximately7.5millionto past 25yearsthenumberofpeoplewithsignificantexposure to from theaircraft. potential noisesourcesaspossible,toholddownthetotal noise noise. Airframedesignerstrytoeliminateasmanyof these noise. Evenstructuraldetailslikerecessedwindowscancreate ered forlandingsandtakeoffs causemixingandcreatemore the relativelyundisturbedair. Similarly, theflapsthatarelow- noise astheairforciblyflowsaroundgearandmixes with inefficiencies. frame noiseiscausedbythemixingofair, butfromaerodynamic the airframebecomesmorepredominant.Likejetnoise,air- added bonus. resultant noise.Thedesignalsoimprovesfuelefficiency, an second streamholdsdownthemagnitudeofmixingand effectively reducingthespeedofairexitingengine.The much fasterthantheairaroundenginebutactsasasheath jet. Thesecondstreamisstill around thehotcentralcore and slowerflowofair creating asecond,cooler, design reducesjetnoiseby the engine. louder therumblingbehind stronger themixingand air exitingtheengine, faster andhotterthejetof engine causesjetnoise.The air movingaroundthe engine withthecold,slow speed jetofairfromthe The mixingofthehot,high- called jetnoise—thedeeprumblingwhenaaircrafttakesoff. speed jetofairthatstreamsouttheback.Thisiscommonly of thejetenginecanreducecompressorwhine. is approachingarunway. Sound-absorbinglinersalongtheinlet inside theengineiscause,mostnoticeablywhenanaircraft whistling fromthefrontofengine.Thespinningmachinery sources. Thefirstiscalledcompressorwhine,thehigh-pitched El Segundo,California. The authorisSeniorStaff Engineer with WyleLaboratories, A varietyofadvanceshavereducedaircraftnoise,andinthe For example,theloweredlandinggearonanaircraftcauses As theenginenoisebecomesquieter, thenoisegeneratedby A high-bypassengine The othersourceofnoisefromajetengineisthehot,high- airframe noiseinflight. Lowered landinggearcontributesto sounds—low-frequency sound propagates farther, with less attenuation, than high-frequency sound; and low-frequency sound penetrates into houses more readily than does high-frequency sound.2

Controlling Aircraft Noise FAA has an ongoing program to reduce the number of noise-sensitive areas exposed to high levels of aircraft noise (2). Airports can conduct a federally funded Part 150 Study to identify actions to reduce aircraft noise in sensitive areas—a federally funded project is not nec- essary to initiate a study. Several methods can limit residential exposure to aircraft noise, including the acquisition by an airport of properties in the highest noise areas—for example, with a DNL greater than 70 or 75 dB from aircraft; houses, schools, and churches can be insu- FIGURE 3 Percentages of county areas in which the sounds of jet traffic are lated for sound; preferred runways can be used, if noticeable during the day. wind conditions permit; flight corridors also can be altered; and cockpit procedures can be developed for the best use of thrust, speed, and climb, to limit TABLE 2 Aircraft Sound Levels and Number of Operations to Produce departure and arrival noise. DNL of 65 dB The success of any of these methods, however, Approximate Approximate depends on trust and good communication with the Time Above Total Time communities and with the aircraft operators. Resi- Maximum Required Number 60 dB(A) Above Sound of Operations in for Each 60 dB(A) dents often do not understand how an airport oper- Level, dB(A) 24 hours Operation in 24 hours ates, how airspace is managed, and the degree of 95 10 50 seconds 8 minutes flexibility that airports, air traffic controllers, and 85 100 35 seconds 1 hour pilots have in managing flight operations. Aviation professionals are realizing the importance of devel- 75 1,000 20 seconds 6 hours oping clear, forthright communication and dialog with residents. tion of the environmental effects of federally funded The distribution of responsibilities complicates projects, the Federal Highway Administration attempts to limit the conflicts between noise-sensitive (FHWA) developed methods to measure, predict, and land use and aviation noise. FAA controls the airspace, control highway traffic noise (3, 4). the pilot is responsible for flying the plane, local juris- dictions determine land use, and the airport meets Roadway Traffic Sound Metric aviation needs and provides convenient passenger ser- FHWA has determined that traffic noise impacts occur vice. These stakeholders must work together to min- when predicted levels of traffic noise approach or imize the noise exposure for noise-sensitive lands. exceed the Noise Abatement Criteria (5). Impacts also can occur when predicted noise levels substantially Noise from Roadways exceed existing sound levels. At high volumes and speeds, roadway traffic can pro- Roadway traffic noise is evaluated with an hourly TR NEWS 240 SEPTEMBER–OCTOBER 2005 duce an almost constant sound level, punctuated by A-weighted equivalent sound level, Leq(h). When increases from noisy vehicles or loud trucks—although the predicted traffic noise for the loudest hour in a noticeable, the increases are not dramatic and are not residential location regularly approaches or exceeds likely to exceed the general level by more than 5 to 10 67 dB(A) Leq(h), noise abatement must be consid- dB. In contrast, the sound of sparse nighttime traffic pri- ered. marily of heavy trucks is a series of single events. To gain funding, an abatement measure must Noise from roadway traffic became a significant reduce noise substantially and affordably. FHWA per- issue in the early 1970s, when the Interstate system mits states to determine the approach-or-exceed level, was extending through cities, towns, and residential the amount of reduction a measure would provide, areas. In response to legislation requiring documenta- and whether the costs are reasonable. 2 A-weighting is a summation of the sound levels across Table 3 provides 1-hour equivalent sound levels frequencies. See sidebar, page 6. measured at 150 feet from the center of a roadway for 9 10 TR NEWS 240 SEPTEMBER–OCTOBER 2005 1 T land useinandaroundairports. aviation noiseandhowtoapplytheinformationimprove decrease aircraftnoiseandreduceemissionsfuelburn. sponses, cognitiveperformance,andsleepquality. a community, includingnoiseannoyance, physiologicalre- developing metricstoevaluatetheimpactofairportnoise on frequency noise. development oftechnologytomitigatetheimpacts low- and analysis;findingscouldleadtoregulatoryaction the aircraft. shaped sonicboomsfroma new classofsupersonicbusiness meet thecontinuingchallengesofaviationenvironmentalissues. space. Thecenteralsowilltrainthenext-generationworkforceto environmental impactsthatchallengethegrowthofcivilaero- ment decisionmakersandindustryexecutivesforaddressingthe involved inaviation. trial, government,community, andprofessionalorganizations research agendawasdevelopedincollaborationwith32indus- of Missouri–Rolla,andYork University. PARTNER’s versity, UniversityofCentralFlorida, State University, PurdueUniversity, StanfordUni- Florida InternationalUniversity, Pennsylvania of Technology asthelead:BoiseStateUniversity, tions andfinancing,withMassachusettsInstitute research results,education,andcenteropera- grated planforresearch,disseminationof and Transport Canadacosponsorthecenter. Aeronautics andSpaceAdministration(NASA), Aviation Administration(FAA), theNational aerospace environmentalissues.TheFederal craft andworkstoenhanceunderstandingof force capabilitiesforquieterandcleanerair- breakthrough technical,operational,andwork- ation EmissionsMitigation.PARTNER fosters Center ofExcellenceforAircraftNoiseandAvi- established inSeptember2003toserveasthe http://partner.aero.      Following aresomeoftheprojectsunderway: PARTNER researchwillprovidecriticalinformationtogovern- Nine universitieshavedevelopedaninte- and EmissionsReduction(PARTNER) was he PartnershipforAirTransportation Noise Land UseandAirportControls,studyingtheeffects of Continuous DescentApproach,devisingproceduresto Measurements, Metrics,andHealthEffects ofNoise, Low-Frequency NoiseStudy, involvingexperimentation Supersonic Transport, investigatingtheacceptabilityof Partnership forAirTransportation NoiseandEmissionsReduction 1 ROBERT J.BERNHARD PARTNER making. noise, emissions,andperformance, tosupportpolicydecision evaluate thetrade-offs attheaircraft systemlevelbetween and collectiveaction. forge policiesandprocessesforenhancedcommunication Office withstakeholdersinaviationandtheenvironmentto actively throughNASA’s JointPlanning andDevelopment goals, andrecommendedactions. ment, outlininganationalvisionstatement,framework for to climatechange. the atmospheretounderstandhowaviationmaycontribute the healtheffects. characterizing aircraftandairportemissionstodetermine nities. al informationaboutaviationnoiseforairportsandcommu- University, West Lafayette,Indiana. The authorisProfessorofMechanical Engineering,Purdue operations, policy, andtheenvironment. aviation andtoevaluateinteractionsbetweentechnology, tools andmetricstoquantifytheenvironmentalimpactsof       

Environmental DesignSpace,developingtoolsto Lateral AlignmentinComplexSystems,workinginter- Report totheU.S.Congress:Aviation andtheEnviron- Valuations andTrade-Offs ofPolicyOptions,developing Aircraft andClimate,modelingtheeffects ofaircrafton Measurements, Metrics,andHealthEffects ofEmissions, NoiseQuest, assemblingawebsiteresourceofeducation-

A L : P DCOCK EE HOTO different traffic mixes and speeds. During any of the TABLE 3 One-hour Equivalent Sound Level at 150 feet from Roadway scenarios, the sound would interfere with speech almost continuously. A 13-foot-high noise barrier 25 Vehicles per Hour Medium Speed, Leq(h) feet from the edge of the roadway would reduce levels Automobiles Trucks Heavy Trucks mph dB(A) by 8 to 9 dB—a noticeable difference that would 1,500 100 200 65 67 improve the audibility of speech communication. 1,500 100 200 50 64 Roadway Noise Issues 1,500 100 0 65 63 The federal government does not have an ongoing 1,500 0 0 65 62 program to reduce the number of homes exposed to high sound levels from street traffic. Some states tinuous walls or earthen hills—that shield noise-sen- independently provide Type II—that is, retrofitted— sitive areas along a right-of-way. To be effective, the noise barriers for roadways. The examination of barriers or berms must be long—often several thou- noise and the design of abatement measures usually sand feet long—and unbroken. occur as a requirement of the environmental process As a result, berms are feasible only along limited- for proposed highway construction or for capacity access highways or long sections of arterials that have improvement projects. few curb-cuts. Most roadway noise analysis and abate- Several approaches are used to control the noise ment therefore focuses on these types of roads and produced by roadway traffic. Most common is the does not address many of the other types of highly construction of noise barriers or berms—high, con- traveled urban or suburban arterials or feeder roads.

Research Projects Target Highway Noise

AMIR N. HANNA P everal National Cooperative Highway Research HOTO SProgram (NCHRP) projects are under way to : FHWA develop products that will help highway agencies measure highway noise, enhance computer analysis of traffic noise impacts, and identify and imple- ment effective means for reducing noise impacts on nearby communities:

 Measuring Tire–Pavement Noise at the Source (NCHRP Project 1-44) is developing ratio- nal procedures for measuring tire–pavement noise from light and heavy vehicles operating at highway speeds and on all types of paved surfaces.  Truck Noise Source Mapping (NCHRP Project 8-56) is applying acoustic measurement and noise TR NEWS 240 SEPTEMBER–OCTOBER 2005 source mapping techniques to identify, locate, from state departments of transportation in a Scan group inspects the and quantify noise sources on the typical com- 2004 scanning tour that reviewed how other sound intensity setup on mercial truck and tractor-semitrailer combina- countries are using quiet pavements to mitigate light vehicle at French test track. tions that operate on U.S. roadways. highway noise (see article, page 16). The tour was  Texturing of Concrete Pavements (NCHRP part of the International Scanning Program of the Project 10-67) will recommend texturing methods American Association of State Highway and to improve the frictional characteristics of con- Transportation Officials, NCHRP, and the Federal crete pavement surfaces, with consideration of Highway Administration. the effects on noise.  Highway Research and Technology: Inter- The author is Senior Program Officer, TRB national Information Sharing (NCHRP Project 20- Cooperative Research Programs, 202-334-1892, 36) supported the participation of professionals [email protected]. 11 12 TR NEWS 240 SEPTEMBER–OCTOBER 2005 T Design Handbook book topicsinclude associated withhighwaynoisebarrierdesign.Hand- tion, addressingacousticalandnonacousticalissues noise barrierdesignsincetheoriginal1976publica- book of NaturalEnvironment. tion SystemsCenterinsupportoftheFHWA Office Facility attheJohnA.Volpe NationalTransporta- 2006. BothtitlesweredevelopedbytheAcoustics Handbook release the and videoinFebruary2000ispreparingto formance, costs,andcommunityacceptance; ations; tures; features; mance; design, includingabriefdiscussionofperfor- nology; The           published the he FederalHighwayAdministration(FHWA) Assessments ofeffectiveness, includingper- Typical designprocesses; Installation, maintenance,andcostconsider- Product evaluation; Utility, structural,andsafetyconsiderations; Aesthetics; Noise barriermaterials,includingsurfacetex- Noise barriertypes,descriptions,andspecial Acoustical considerationsofnoisebarrier Overview, historicalperspective,andtermi- package reflectsimprovementsandchangesin FHWA HighwayNoiseBarrierDesignHand- with accompanyingCD-ROMinearly FHWA HighwayConstructionNoise Updated GuidesforControlling HighwayNoise FHWA HighwayNoiseBarrier with accompanyingCD-ROM

HARVEY S.KNAUER

: FHWA : P HOTO ogy; construction noise.Topics include nonacoustical issuesassociatedwithhighway-related nal 1976publication,coveringacousticaland book feature. mote orrecommendanyparticulartypeofbarrier design ofnoiseabatementfeaturesbutdonotpro- materials presentavarietyofconsiderationsinthe and individualsinvolvedinnoisebarrierdesign.The are intendedasanaidtoagencies,organizations, not representFHWA policyonnoiseabatementbut design. construction projects. plified predictionmodelfornoise levelsontypical nation. using avarietyoftechniques;and als, trainingprograms,andreferences; tacts; ences, includingasearchabledatabaseandcon- ment; and rangesforbothstationarymobileequip- well ascontractspecificationsandprovisions; of operations,andenforcement-relatedissues,as ing considerationofthetimeperiod,duration source, alongthepath,andatreceptor, includ- methodology andimpactevaluation; interpretation ofdata; construction noise,includingtheprocessingand wildlife; Acoustics, Inc., Harrisburg, Pennsylvania. The authorisVice President,Environmental The The handbookandtheassociatedmaterialdo Under developmentwiththehandbook isasim-             Tools andinformationresourcestoaidin Interagency, intra-agency, andothercoordi- Public involvementduringtheprojectphase, Related trainingmaterials,includingmanu- A compendiumofconstructionnoiseexperi- Data forconstructionequipmentnoiselevels Mitigation ofconstructionnoiseatthe Prediction ofconstructionnoise,including Operations andequipmentformeasuring Construction noisecriteriaandmetrics; Effects of constructionnoiseonhumansand Introduction, background,andterminol- akg loreflectsadvancessincetheorigi- also package FHWA HighwayConstructionNoiseHand- Because barriers can cost up to $20 per square URPHEY foot—or more than $1 million per mile—a signifi- C ED cant number of homes must benefit to justify the : T HOTO expenditure. Low-density residential areas—such as P rural areas or large-lot suburban locations—are less likely to qualify for barrier construction than are high-density areas. Moreover, most states will not build a noise barrier without the residents’ concurrence. Sometimes a few residents pressure a highway agency, money is allo- cated, and a study is conducted, but public meetings reveal that a majority of the residents would prefer traffic noise to a long, high wall. Several state agencies have conducted studies to set priorities for barrier construction; this approach minimizes the number of disputes about which neighborhoods along a highway will have barriers. The method involves measuring sound levels; com- puting the loudest hours throughout the corridor; determining the barrier locations, heights, and costs; and identifying the number of homes that will benefit in each neighborhood according to the number of the right-of-way or even above the right-of-way for Freight train passes over decibels reduced. underground transit, so that vibration of structures I-90 at Latah Junction, The policy ranks the neighborhoods by the cost is likely. Along surface rail lines, the proximity of Spokane, Washington. per home benefited. The barriers are built in order of residences makes the sound levels and the vibra- priority, with the timing determined by the availabil- tions an issue. ity of funds. In response to environmental legislation, the Fed- eral Railroad Administration (FRA) and the Federal Controlling Roadway Noise Transit Administration (FTA) have developed meth- The usual methods for limiting roadway noise include ods to measure, predict, and control noise and vibra- building barriers or berms, establishing traffic con- tion from rail and rapid transit. The methods are trols such as speed limits, altering vertical or horizon- applied as part of the environmental documentation tal alignment for new roadways, establishing buffer required for federally funded projects. zones along a right-of-way, and using quiet pave- Agencies are addressing ment—a recent innovation. Rail Sound Metrics noise and vibration from Barriers are the most common solution for pro- FRA and FTA have published guidance manuals with elevated transit rail in tecting outdoor areas, when justified by the step-by-step directions for preparing assessments of urban neighborhoods. cost–benefit. Sound insulation sometimes is chosen, ORG

particularly for schools, and quiet pavement is gain- -L. ing interest, as indicated by many research projects in HICAGO the United States and abroad (see related articles on : C HOTO pages 16 and 18). P TR NEWS 240 SEPTEMBER–OCTOBER 2005 Rail Noise Rail transportation generates sound and vibration levels that can be significant. Although low-frequency sound from aircraft can produce vibration in structures, and elevated highways or roads on certain kinds of geological formations also can produce vibrations that travel through the ground and affect structures, these circumstances are too rare or too isolated to be included in any routine analysis. In contrast, rail generates ground-borne vibrations throughout the right-of-way. In densely populated areas, buildings often are located close to 13 depend on the number of events—more than 70 events per day is considered frequent, and fewer than 70, infrequent. The lowest threshold is for buildings that require a low ambient vibration for operation—for example, buildings with equipment such as electron micro- scopes or with sensitive manufacturing processes. This lowest threshold is roughly equivalent to the threshold for human perception. Higher thresholds are used for residences and yet higher for institu- tions with daytime-only uses.

Rail Noise and Vibration Issues Rail systems include a variety of noise sources—some are associated with the operation of rolling stock, such as locomotives and rail cars, horns and whistles, and wheel squeal on tight curves, but many ancillary sound sources also may contribute. Some are related to rail operations, such as crossing signals, crossovers FIGURE 4 Noise impact determination for rail projects. and switches, substations, and locomotive idling, but others are from the transportation modes that tie into rail noise and vibration (6–7). Like FAA, both agen- the rail system, such as buses and automobiles at sta- cies use DNL as the metric to determine the impacts tions and in park-and-ride lots. of rail noise; like FHWA, both also use Leq(h). Horns for grade crossings can be a problem for DNL is used to measure the effects on resi- nearby residents (see box, page 24). The air horns on dences. The Leq(h) for the loudest hour of the day freight and some commuter rail locomotives vary in applies to other noise- and vibration-sensitive uses. sound levels. Although engineers signal the same FRA and FTA identify two levels of noise impact— “two longs, a short, and a long,” the duration impact and severe impact—based on the sound lev- depends on the operator and can affect different els from the proposed rail project and the sound numbers of homes along a right-of-way. Current levels before the project (Figure 4). Table 4 shows research is examining the use of horns that are per- some relationships between DNL values and types manently mounted at crossings and that sound auto- of trains at different speeds. matically as a train approaches. Figure 4 shows how rail noise impacts are deter- Locomotives often idle for long periods or mined. Category 1 lands require quiet but are used overnight at termini in suburban areas. Sometimes mainly during the day; therefore the sound is mea- these idling locations must be moved to accommodate sured in Leq(h). Category 2 lands include residences; changes in operations or schedules, and residential DNL is the metric. Category 3 lands have institu- areas with no previous rail noise exposure are sub- tional uses with daytime and evening activities, jected to the sound of an idling locomotive for hours which are deemed to be 5 dB less sensitive to project or overnight. noise than lands in Categories 1 and 2. Older engines could not always be restarted and Rail vibration impact thresholds are determined had to idle, but modern locomotives are designed to from an absolute level. The thresholds of impact shut down, sometimes automatically after a period of

TABLE 4 DNL for Different Types of Trains, 50 feet from Track

Number of Trains per hour DNL Type of Train Speed Day Night at 50 feet 4-car rapid transit 50 mph 20 2 65 dB 4-car rapid transit 20 mph 20 2 60 dB 8-car, 1-locomotive commuter 60 mph 1 0 55 dB TR NEWS 240 SEPTEMBER–OCTOBER 2005 TR NEWS 240 SEPTEMBER–OCTOBER 8-car, 1-locomotive commuter 20 mph 1 0 50 dB 14 idling, and are quieter as well. Idling not only produces Sound levels and vibration levels can be reduced by noise but consumes fuel and releases air pollution, grinding the wheel and rail surfaces. Irregular sur- adding to the reasons to reduce the idling times. faces, flats produced when wheels lock in stopping, and rough wheels or rails can increase a train’s sound Controlling Rail Noise and Vibration and vibration levels. Wheel truing—eliminating flat If an analysis indicates an impact or a severe impact spots and assuring the roundness of the wheels—and from rail noise or vibration, mitigation alternatives proper grinding of rail profiles can be costly. Rail grind- must be evaluated. On projects that include the pur- ing may require extensive analysis to ensure that the chase of new vehicles, an effective measure may be to final contours of the surfaces will be durable. develop vehicle design specifications. Other methods Noise barriers can be effective for at-grade and ele- to reduce impacts include the design or retrofitting of vated rail lines. The barriers can be located close to the track support systems, the maintenance of wheels and rail line and need not be high if the wheel–rail inter- rails, the construction of noise barriers, and the use of action is the primary source of noise. On elevated rail sound insulation for buildings. lines, barriers 4 feet high can be effective. In addition, When vibration levels are the source of the impact, if barriers are not feasible—for example, near grade changing the track support system can be effective— crossings—installing sound insulation in nearby a “floating slab,” a resiliently supported concrete slab houses may be a solution. to which the tracks are fastened; resilient rail fasteners; and resilient mats under the ballast or concrete ties References supported by rubber pads are methods to reduce 1. Miller, N. P. Transportation Noise and Recreational Lands. ground vibrations. Subway projects frequently use Noise News International, Volume 11, Number 1, March 2003. http://www.hmmh.com/presentations.html/N011.pdf. these techniques. Vibration problems are less com- 2. Airport Noise Compatibility Planning, Code of Federal Regu- mon for at-grade and elevated track. lations, Title 14, Volume 3, Part 150, January 1, 2005. 3. Anderson, G. S., C. S. Y. Lee, G. G. Fleming, and C. W. P HOTO Menge. FHWA Traffic Noise Model User’s Guide. FHWA Report : W No. FHWA-PD-96-009, Federal Highway Administration, TR NEWS 240 SEPTEMBER–OCTOBER 2005 ILSON January 1998. . I

HRIG 4. FHWA Traffic Noise Model User’s Guide: Version 2.5 Addendum.

, Federal Highway Administration, April 2004. www.traffic- AND noisemodel.org/downloads/TNM25UsersGuideAdden- A SSOCIATES dum.pdf. 5. Federal Highway Administration, 23 CFR Part 772: Proce- dures for Abatement of Highway Traffic Noise and Con- struction Noise—Final Rule. Federal Register, Volume 70, Number 62, April 1, 2005. 6. High-Speed Ground Transportation Noise and Vibration Impact Assessment. Report No. 293630-1, Federal Railroad Admin- istration, December 1998. http://www.fra.dot.gov/us/con- tent/253. Portland TriMet transit rail passes between a sound- 7. Transit Noise and Vibration Assessment. DOT-T-95-16, Federal absorbing wall and a sound barrier wall. Transit Administration, April 1995. 15 16 TR NEWS 240 SEPTEMBER–OCTOBER 2005 R loading tothewheel,inlinewithtiretracks. intensity setuponaheavyvehiclethatcanvary In theUnitedKingdom,TRITONusesasound Administration, Washington, D.C. specialist withtheFederalHighway The authorisahighwaytraffic noise ties, thintexturedsurfaceswere foundto high-speed facilities.Onlow-speed facili- layer anddouble-layerporousasphalton methodologies andmonitoringsystems. information onnoisemeasurement tices. Inaddition,theteamgathered systems andidentifiedinnovativeprac- nance, andmonitoringofquietpavement practice indesign,construction,mainte- National Transportation SystemsCenter. the AcousticsFacilityatVolpe tation, privateindustry, academia,and FHWA, statedepartments oftranspor- issues andincludedmembersfrom had experienceinnoiseandpavement Research Program.The14participants the NationalCooperativeHighway ning ProgramofAASHTO,FHWA, and ducted aspartoftheInternationalScan- United Kingdom.Thetourwascon- Netherlands, France,Italy, andthe 30–May 16,2004,visitingDenmark,the Quiet PavementTechnologies, April participated inanInternationalScanof and Transportation Officials (AASHTO) American AssociationofStateHighway The groupexaminedsectionsofsingle- The tourdocumentedthestateof way Administration(FHWA) andthe epresentatives oftheFederalHigh- Scanning Tour ExaminesTechnologies andExperience asphalt fromDenmark. Core samplesofdouble-andsingle-layer porous tions inconstruction,aggregateselec- ment beconsidered?Forexample,varia- affect noisereductiononaquietpave- adjustment orintermsoffrequency? for noisereduction—asanabsolute ments overtime. not havethefundstomonitorpave- strated longevity. Severalcountriesdid experimental typeshavenotyetdemon- were notedforsomepavements,many Although noisereductionsovertime heavy vehicles? ment onlightvehiclescomparedwith ment? bilities ordoesitdamagethepave- ments renewthenoisereductioncapa- measurement? methods andthewaysideof the close-proximityorsound-intensity side? ments fromthereceptoratway- tire–pavement interactionormeasure- sound-intensity measurementsatthe was mosteffective: close-proximityor research: demonstrated theneedforfurther other considerations. crete pavementbecauseofclimateor served wellincountriesthatselectedcon- and diamond-groundconcretesections be successful.Exposedaggregateconcrete Quiet PavementAbroad        Several issuesnotedduringthescan How canallthemanyfactorsthat What isthebestwaytoaccount How durablearethepavements? What aretheeffects ofquiet pave- Does thecleaningofporouspave- What arethecorrelationsbetween Which measurementmethodology CHRIS CORBISIER qpppeml.htm. 1 measurement bytheclose-proximitymethod. Trailer usedintheNetherlandsforsound quiet. strating thatapavementqualifiesas the researchrequirementsfordemon- produce practicalresults. assess progress,andguidetheresearchto Coordination isessentialtoavoiderrors, cation amongstakeholdersisimportant. and isinthebeginningstages,communi- stakeholders, includesmanyvariables, quiet pavementresearchinvolvesmany flexibility torunitsownprogram.Because United States,whereeachstatehasthe communication andcoordinationinthe considerations. as differing environmental andeconomic ferent conclusionsfromresearch,aswell country haddifferent experiences anddif- success, moreresearchisneeded.Each eter pavementscanbeimplementedwith considered. before noisereductioncapabilitiesare satisfy safetyanddurabilityrequirements reduction. Moreover, thepavementmust reference pavementcanaffect thenoise nique, pavementthickness,andtypical ment temperature,measurementtech- tion, climate,vehicletypes,binder, pave- accurate comparisonofdataand trends. ments, stakeholderswillfacilitate the www.fhwa.dot.gov/environment/noise/ FHWA hasdraftedamemorandumon The scanunderscoredtheneedfor The scanshowedthatalthoughqui- 1 By adheringtotheserequire-