Retrospective Cost Saving Comparison Between TNM 2.5 and TNM 3.2 Barrier Analysis Results

Abstract

In December of 2021, the Federal Highway Administration (FHWA) Traffic Noise Model (TNM) version 3.1 was released to the public for use on traffic noise projects and subsequently updated to version 3.2 in December 2023. However, most or all state Departments of Transportation (DOT) continue to accept and prefer the use of TNM 2.5 (released in 2004). A presentation at NoiseCon 2023 (TNM 2.5 vs TNM 3.1 Noise Level Prediction Comparison by Mukul Pal and Michael Parsons) came to the conclusion that, generally, TNM 2.5 tends to overpredict traffic noise levels in comparison to the TNM 3.1, resulting in additional impacts and subsequent additional mitigation that may not be necessary when analyzed with the updated algorithms. In this paper, the authors determine potential cost savings by migrating from TNM 2.5 to TNM 3.2 by comparing results from previously approved traffic noise projects. By determining the potential cost savings of a migration, DOTs may be better informed about whether or not they should continue to utilize TNM 2.5 or make the transition to TNM 3.2.