TNM VERSION 2.5 ADDENDUM toValidation of FHWA?s Traffic Noise Model (TNM): Phase 1

The Volpe Center Acoustics Facility (Volpe) in support of the Federal Highway Administration(FHWA) is conducting a multiple-phase study to assess the accuracy and make recommendations onthe use of FHWA’s Traffic Noise Model (TNM). The TNM Validation Study involves highway noisedata collection and TNM modeling for the purpose of data comparison. In 2002, Volpe completedPhase 1 of the study. For this phase, over 100 hours of traffic noise data were collected atseventeen highway sites around the country. The seventeen sites included: open areas next tothe highway with acoustically soft ground (e.g., lawn); open areas with acoustically hardground (e.g., pavement or water); and areas next to the highway with an open area behind asingle noise barrier. Results indicated that TNM Version 2.0 was, on average, over-predictingwhen measured sound level data were not calibrated using a reference microphone, i.e., whensite bias was not accounted for.