The objective of this research was to supplement existing guidance on applying the TNM by identifying best practices to accurately, consistently, and efficiently model (1) structure reflected noise; (2) bridge expansion joints; (3) signalized interchanges; (4) intersections; (5) area sources, e.g., weigh stations, park and ride lots, toll facilities, and service plazas; (6) median barriers; and (7) roundabouts. This research will determine the sensitivity and accuracy of methods to model (1) multi-lane highways, (2) rows of buildings, (3) topography, (4) ground zones, and (5) tree zones, and identify best practices for input parameters. This research also synthesizes the state of practice for analyzing the effects of (1) wind direction and (2) temperature inversion on sound propagation. This research project’s results are intended for use by experienced analysts, modelers, and designers.
STATUS: The revised final report has been published as NCHRP Report 791
Supplemental Guidance on the Application of FHWA’s Traffic Noise Model (TNM) . The report is available
HERE. The report includes the following 12 Appendices that are available
only online:
Appendix A Structure Reflected Noise and Expansion Joint Noise
Appendix B Signalized Interchanges, Intersections and Roundabouts
Appendix C Area Sources
Appendix D Median Barriers
Appendix E Multi-Lane Highways
Appendix F Building Rows
Appendix G Topography
Appendix H Ground Zones
Appendix I Tree Zones
Appendix J Wind and Temperature Gradients
Appendix K Parallel Barriers
Appendix L Tunnel Openings
BACKGROUND
Noise is an important environmental consideration for highway planners and designers, and through 2007, state highway agencies have spent $4.5 billion to abate the noise generated by federal-aid highway projects. Transportation agencies measure different aspects of highway noise to determine or predict community impacts during transportation planning although measurement instrumentation and procedures have varied from program to program and agency to agency. Precise, uniform, field measurement practice allows for valid comparison of results from similar studies performed by a variety of transportation practitioners and researchers. To aid states in complying with FHWA’s noise policies and regulations, FHWA developed and improved a series of computer models beginning in the 1970s. The current model, FHWA’s Traffic Noise Model (TNM) is a computer program used for predicting noise impacts in the vicinity of highways, and it uses advances in personal computer hardware and software to improve upon the accuracy and ease of modeling highway noise, including the design of effective, cost-efficient highway noise barriers.
FHWA has provided substantial guidance for the routine application of TNM but scenarios exist for which there is no technical guidance. Out of necessity and without technical guidance, TNM users have independently developed techniques to assemble and input data into the TNM to analyze these scenarios. Typically these techniques have not been validated with field measurements, and the accuracy of their results is unknown.
