In March 1998, the Federal Highway Administration (FHWA) Office of Natural Environment, released the FHWA Traffic Noise Model (FHWA TNM) Version 1.0, a state-of-the-art computer program for highway traffic noise prediction and analysis. Since then, the FHWA, with assistance from the Volpe Center Acoustics Facility (Volpe Center) and Foliage Software Systems (FSS), have released updates of TNM (Versions 1.0a, and 1.0b) in March 1999 and August 1999, respectively. In support of the FHWA and the California Department of Transportation, the Volpe Center and FSS released Version 1.1 in September 2000. TNM 2.0 is the latest release of the TNM software. Two companion reports were released with TNM Version 1.0, a Technical Manual that describes the acoustics within TNM and a User's Guide. In addition, prior to TNM release, a data report was published that describes the vehicle noise-emissions data base within TNM. This document is an addendum to the FHWA TNM Version 1.0 User's Guide. It details the enhancements in the program up to and including Version 2.0.