As part of a multi-year contract, STI provided Caltrans with technical support for air quality analyses in the transportation context. Work includes significant AERMOD dispersion modeling for transportation projects, as well as the development of guidance documents and training classes on AERMOD use. Example projects include the development of best practices materials on configuring roadway sources in AERMOD, case study analyses on preparing meteorological data for AERMOD use, the development of a tool for processing mobile source emission data for input to AERMOD, and the presentation of two-day training classes on applying AERMOD in PM hot-spot analyses.