Transit agencies are subject to both nationwide and local emissions regulations. The Westchester County Department of Transportation (WCDOT) is required to bring its older buses into compliance with county regulations. This paper quantifies emissions reductions resulting from actions taken by WCDOT through an emissions reduction program starting in 2005, with projections up to 2009. Selected buses were tested by the West Virginia University (WVU) Transportable Chassis- Dynamometer Emissions Laboratory over the OCTA cycle and a custom WCDOT driving schedule, the Bee-Line cycle. Based on measured results, future fleet-wide emissions were estimated for two scenarios : a baseline scenario in which the county requirements are met just in time, and a proactive scenario which reflects early actions taken by WCDOT. The proactive approach of WCDOT towards emissions reduction was shown to save, over the five-year period, 112.5 tons (53%) of carbon monoxide (CO), 23.3 tons (1%) of nitrogen oxides (NOx ), 11.3 tons (30%) of hydrocarbons (HC), 7.3 tons (44%) of particulate matter (PM), 1,119 tons (1%) of carbon dioxide (CO2 ), and 114,000 gallons (1%) of diesel fuel.