Supplemental Guidance on the Application of FHWA’s Traffic Noise Model (TNM)

Abstract

Beginning in the 1970s, the Federal Highway Administration (FHWA) developed and improved a series of computerized noise prediction models to aid states in complying with FHWA’s noise policies and regulations. FHWA’s Transportation Noise Model is a computer program used for predicting noise levels and therefore 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. In this project, best practices and supplemental existing guidance were identified on applying TNM to accurately, consistently, and efficiently model structure-reflected noise; bridge expansion joints; signalized interchanges; intersections; area sources (e.g., weigh stations, park and ride lots, toll facilities, and service plazas); median barriers; and roundabouts. This research determined the sensitivity and accuracy of methods to model multilane highways, rows of buildings, topography, ground zones, and tree zones, and identified best practices for input parameters. The research also synthesized the state of practice for analyzing the effects of wind direction and temperature inversion on sound propagation. The report is organized by scenario, and experienced transportation analysts, modelers, and designers should find this guidance immediately useful in using TNM to model noise impacts under these scenarios.