NBSIR 75-77l(/?7 An Evaluation and Assessment of Existing Data and Procedures for the Measurement of Noise from Buses Applied Acoustics Section Institute for Basic Standards National Bureau of Standards Washington, D. C. 20234 September 1975 Final Report Prepared for Office of Noise Abatement and Control U. S. Environmental Protection Agency Washington, D. C. 20460 NBSIR 75-771 AN EVALUATION AND ASSESSMENT OF EXISTING DATA AND PROCEDURES FOR THE MEASUREMENT OF NOISE FROM BUSES Applied Acoustics Section Institute for Basic Standards National Bureau of Standards Washington, D. C. 20234 September 1975 Final Report Prepared for Office of Noise Abatement and Control U. S. Environmental Protection Agency Washington, D. C. 20460 U.S. DEPARTMENT OF COMMERCE, Rogers C.B. Morton, Secretary James A. Baker, III, Urtder Secretary Dr. Betsy Ancker-Johnson. Assistant Secretary for Science and Technology NATIONAL BUREAU OF STANDARDS. Ernest Ambler. Acting Director Tatle of Contents Page Executive Suiimiary ii 1. Introduction and Scope 1 2. Bus Description and Design 2 2.1. Definition 2 2.2. Industry Structure 2 2.3. Design Characteristics k 3. Effects of Noise and Parties Affected 5 k. Major Noise Sources $ 5. Modes of Operation Y 6. Existing Measurement Procedures 7 6.1. Exterior Noise 7 6.2. Interior Noise 10 7. Data Base and Correlations 12 8. bverviev of Bus Noise Measurement Difficulties I3 8.1. Classification I3 8.2. Relation of Physical Measures to Effects/Normal Use .... 13 8.3. Quantity Measured ik . 8.U. Acoustic Environment I5 8.5. Instr-jmentation I6 8.6. Alternative Test Procedures I7 9. Appendix A. A Discussion of Bus Subsource Noise I8 10. Appendix B. Existing Bus Noise Measurement Procedures 2U 11. Appendix C. Bus Noise Reduction: Domestic and Foreign 39 12. References 39 13. Bibliography k2 i , Executive Summary EPA is charged -with taking strong, comprehensive action to protect public health and welfare from increasing noise. Accordingly, the Agency initially identified medium and heavy trucks and portable air compressors as major noise sources and promulgated noise emission regulations covering these products. Additional products have recently been identified as major noise soiirces, including buses. For the purposes of this discussion- buses can be defined as motor vehicles (other than taxicabs) designed for carrying more than ten passengers which are used for the transportation of persons for compensation, including intracity, intercity, school and specialty buses. As was the case for medium and heavy trucks, bus noise can be categorized as the noise produced by the power plant [including the engine, exhaust, intake, cooling fan, etc.] and by the tire-road interaction. The noise from the power plant increases as the engine speed (and power) increases while the noise from tires increases as the vehicle speed increases. Maximiom power-plant noise usually occurs when the engine is delivering maximum power at its maximum operating speed. The percentage of time a bios spends at maximum noise conditions is determined by the vehicles power-to-weight ratio and operating conditions such as acceleration, speed, load, grade and to some extent, the manner in which the bus is operated. This report reviews existing bus noise meas\irement procedures with regard to their usefulness in the regulation of bus noise as well as the availability, extent and applicability of existing data. On the basis of this review, the following probable or potential measurement difficulties have been identified that could hinder the promilLgation and/or enforcement of future EPA regulations to control the noise emission from buses. m- M ALMOST NON-EXISTENT DATA BASE . Very limited data exist in the public domain on the noise levels associated with bus operations. This is due, in part, to the fact that in the United States, medium and heavy duty trucks and buses are tested according to the same test procedure which has associated with it a single recommended sound level to be met by both trucks and buses . Since mediimi trucks and buses tended to be quieter than heavy trucks under the operational test conditions specified — low speed acceleration passby (high engine speed, low vehicle speed) — the majority of the emphasis has been placed on research and development programs aimed at reducing heavy truck noise. LACK OF TYPICAL USAGE DATA . In order to develop an appropriate reliable and repeatable test procedure, it is necessary to consider the range of possible bus operational modes. What is needed is definition of the percentage of time which a bus typically spends at idle, accelerating, decelerating, at low speed cruise, at high speed cruise, at wide open throttle, etc. Such typical usage data do not presently exist for buses. :nZj 10 COI^SIDER a CUKBSIDE test , since nany of the people affected "by cus ncise are out-cf-docrs and in close proxiiiity to the "buses, the noise levels to vhich they are exposed can "be much higher than those typically meas'ored "by existing U. S. standard procedures vhich utilize a measurement location 50 feet (15-2 m) from the centerline of the bus. There exists a need to develop a cur"bside test to assess impact of noise on pedestrians and for correlation of such data with conventional [50 foot (15-2 m) ] data to determine if both tests are needed. -~y^' m TC DF/ELCP Air 117- VEHICLE TEST . There exists a need to develop an in-vehicle test to assess the impact of noise on passengers. (Bus drivers are covered under the Bureau of Motor Carrier Safety Regulations vhich establish a maximum interior sound level for buses operated in interstate commerce. Presumably the remainder of the bus drivers vould be covered by the OSHA regulations.) liEED TO ACCCU:;T FOR EKyXROHIMTAL/SnE EFFECTS . There is a need for t"ne various envircr-mental and test site effects on noise generation, radiation and/or propagation to be systematically investigated and correction factors developed so t'nat meas-jjrements made -jr.der any conditions may be corrected to a single standard set of conditions. If correction factors are not feasible then there is a need for a site calibration procei-^e or definition of limiting test conditions. I"": 70?. SDTLE?. TEST PRGCEL'Jr.E . Tnere exists a need to develop a test proced'jre that is simpler to perfcm and is less dependent on veather and test site variables. Correlation should be established betveen the results obtained utilizing such a test and h-oman response to bus noise. a KEED TO SPECIFY z?j^',siii7z pzspciTSE Cr i:;st?.u:.z:;tatic:; more accu?^~eiy . There exists a need to measure the response of existing instr-jmentation to actual transient signals, e.g., a bus passby, in order to establish the interrelationships among the various precision instruments , to supply data to strengthen existing standards, and to establish a data base so that the technical community, manufacturers, lavmakers and enforcement agencies vill have a common basis for comparison of res-'olts obtained using supposedly comparable eq_uipment. In summary, it is doubtful that the data in the open literature are extensive enough to provide EPA vith the information needed for a comprehensive analysis of the economic costs and technical feasibility associated vith a given regulation. Furthermore, there are practically no data available upon vhich to base an evaluation of alternative bus noise measurement procedures or to establish correlations betveen the noise associated vith various operational modes and the noise measured utilizing various test procedures. Thujs, it appears that EPA should generate an extensive physical data base and investigate alternative meastirement procedures prior to formulation of t'ne Notice of Proposed Rule ''taking. An Evaluation and Assessment of ExinLing Data and Procedures for the Measurement of Noise From Buses This report reviews existing "bus noise measurement procedures with regard to their usef\iLness in the regulation of "bus noise as well as the availability, extent and applicability of existing data. On the basis of this review, probable or potential measurement difficulties are identified that could hinder the promulgation and/or enforcement of future EPA regulations to control the noise emission from buses. Key Words: Acoustics (sound); bus; measurement methodology; noise emission standard, noise measurement. 1. Introduction and Scope The National Bureau of Standards (NBS), Tonder the sponsorship of the Office of Noise Abatement and Control (ONAC), U. S. Environmental Protection Agency, has attempted to identify probable or potential measure- ment difficulties that could hinder the promulgation and/or enforcement of future noise reg\ilations to control the noise emissions from buses. A search of the open literature in conjunction with numerous personal contacts established the basis for discussion of: 1. The basic characteristics of bus design and construction. 2. The effect of bus noise and the parties affected. 3. The major component noise sources for buses. k. The normal or typical mode of operation characteristic of the various classes of buses. 5. The usefulness of existing measurement procedures for regulation of the noise from buses considering the viewpoint of EPA, manu- facturers and enforcement personnel. 6. The availability, extent and applicability of existing data that coiald be utilized by EPA in their efforts to promulgate noise emission regulations for buses. This report is limited to those factors affecting the measurement of bus noise. EPA/ONAC will independently investigate the technical feasibility and economic implications of bus noise regulation. Also, it is assumed that the strategy followed during the development of the new truck regulation — namely, that tires will be identified separately as a major noise source — will apply to all vehicular noise sources; therefore, this report concentrates on measurement procedures for measuring the noise of buses, excluding tires. 2. Bus Description and Design 2.1. Definition The P'ederal Highway Administration, U.