Emissions from Conventional and Hybrid Electric Transit Buses Tested on Standard and San Francisco Specific Driving Cycles 2002-01-3117

California Air Resources Board's transit bus fleet regulation required public transit fleets in California to reduce emissions starting in 2002 [1]. In response to this rule, San Francisco Municipal Railway (Muni) launched the “Alternative Fuel Pilot Project”. The objective of the project is to compare the on-road performance, emissions, maintainability, safety, and costs of advanced diesel and alternative fuel buses over a two-year period. This paper discusses the preliminary emissions results from chassis dynamometer testing conducted during the first six months of the emissions study. The California Truck Testing Service's dynamometer facility tested four types of buses: conventional diesel, conventional diesel with particulate traps, compressed natural gas, and hybrid-electric transit buses. Vehicle emissions (carbon monoxide (CO), oxides of nitrogen (NO_x), total hydrocarbons (THC), methane (CH₄), and particulate matter (PM)) and fuel economy were measured over the Central Business District (CBD) and New York Bus (NY Bus) driving cycles. Testing was also conducted on a specially-designed San Francisco Route (SF Route) Cycle. This cycle was constructed from speed-time-grade data collected during on-road operation of Muni buses. The results showed that operation on the SF Route Cycle produced NOx emissions and fuel economy levels similar to those of the NY Bus Cycle. On the SF Route Cycle, there was less difference in fuel economy between the different buses. The localized effects of grade were large. For example, on the 19% grade, all the buses produced approximately twice the amount of NOx than on the flat terrain. A representative cycle and emissions model are under development. These will be used to estimate the emissions and fuel economy on individual routes as well as the total on-road transit bus emissions in San Francisco.