The National Academies

NCHRP 08-56 [Completed]

Truck Noise-Source Mapping

  Project Data
Funds: $496,889
Research Agency: Wyle Laboratories, Inc.
Principal Investigator: Kenneth Plotkin
Effective Date: 8/25/2005
Completion Date: 12/31/2008
Comments: Published as NCHRP Report 635


Heavy trucks are significant contributors to overall traffic noise levels, and transportation agencies must better understand the location and relative levels of the principal noise sources (e.g., exhaust, mechanical, tire/pavement, and aerodynamic) on heavy vehicles in order to more successfully mitigate traffic noise impacts.

Typical measures used to mitigate highway traffic noise include noise barriers, land use planning, and insulation of structures. Some transportation agencies are investigating additional measures, such as quiet pavements. Newer acoustical measurement and mapping techniques such as beamforming show promise for isolating the location and extent of the primary noise sources emanating from heavy trucks. Some studies suggest that near-field acoustical holography is a good complement to beamforming for measurement and mapping of low-frequency sounds. Data obtained in this project could directly support a number of ongoing quiet pavement research studies, including the FHWA Quiet Pavement Pilot Project. The data will also yield information that could greatly enhance computer analysis of traffic noise impacts that are a part of environmental impact reports. Information from this project will guide decisions made at both a management level and a project design level.


The objective of this study was to use acoustic measurement and noise-source mapping techniques to accurately identify, locate, and quantify the noise sources on typical commercial truck and tractor-semitrailer combinations operating in the U.S. roadway environment.

TASKS (1.) Conduct a critical analysis of domestic and international published literature, research in progress, and current practice on the basis of applicability, conclusiveness of findings, and usefulness for the analytical needs of this study. This effort should include a review of material related to all aspects of heavy truck noise sources, as well as best available acoustic measurement and noise-source mapping techniques for road, rail, aviation, and other transportation vehicles. (2.) Based on the Task 1 review, develop an experimental design for controlled tests to identify, locate, and quantify the noise sources on heavy trucks at highway speeds. The experiment should be structured in such a way that the results will be applicable to real-world vehicle and traffic conditions. It is expected that the experiment will use one or more acoustic measurement and noise-source mapping techniques and, within the constraints of the project budget and schedule, will control for factors such as the following (listed in priority order):
  • Pavement material and texture (including both dense- and open-graded asphalts and transversely tined Portland Cement Concrete);
  • Vehicle exhaust height (vertical vs. under frame);
  • Truck configuration (including at a minimum two loaded vehicles with different axle and trailer configurations)
  • Tire type/tread pattern;
  • Vehicle speed (e.g., ranges between 10 and 70 mph);
  • Steady vehicle speed (e.g., 60 mph) versus accelerating or decelerating (use of engine brakes);
  • Engine size;
  • Aerodynamic variations (e.g., "shrouded" versus open tractor designs); and
  • Vehicle exhaust condition (e.g., altered, detached, or poor condition).

At a minimum, the noise mapping should be done at the maximum overall A-weighted sound pressure level measured in decibels during pass-by. The output data should delineate the distribution of relative sound pressure levels (both unweighted and A-weighted) of the major truck noise point sources. Data should be presented both numerically and graphically using color contour maps.

(3.) Conduct a proof-of-concept test of the proposed noise measurement systems and noise-mapping techniques. (4.) Submit an interim report, within 12 months, to document Tasks 1 through 3 for review by the NCHRP. The contractor will be expected to meet with the NCHRP approximately 1 month later. The contractor shall not begin work on the remaining tasks without NCHRP approval. (5.) Execute the testing plan as approved by the NCHRP. (6.) Document and analyze the results of the Task 5 tests to identify, locate, and quantify the noise point sources on heavy trucks. (7.) Summarize the key findings about the relative contributions of heavy truck noise sources in the context of variables studied in Task 5. (8.) Identify areas where further research and testing are needed to improve our ability to identify, locate, and quantify truck noise sources. These could include the investigation of additional variables or means of improving noise measurement and mapping techniques. (9.) Submit a final report that documents the entire research effort. In addition, provide a PowerPoint presentation summarizing the background, objectives, research method, results, applications, and benefits.

Product Availability: NCHRP Report 635: Acoustic Beamforming: Mapping Sources of Truck Noise.

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