Development of a grade sensitive transit bus driving cycle in San Francisco (California)

Emissions and fuel economy are often quantified on chassis dynamometers following established driving cycles because on-road measurement are costly and irreproducible. These driving cycles are speed versus time traces and all existing cycles assume no road gradient. It is well documented that moderate grade leads to significant increases in diesel vehicle emissions of oxides of nitrogen (NOx) and particulate matter (PM). Therefore, the diesel vehicle emission models and emissions estimates based on these driving cycles and chassis test results are inaccurate for cities, such as San Francisco (SF), which have steep and undulating terrain. This dissertation presents a first attempt to develop grade sensitive driving cycles for diesel buses operating in SF. The methodology, a combination of stratified random sampling for route selection, instrumented vehicle data collection, random selection of cycle generation, and Root Mean Square (RMS) error and first-introduced information value (IV) comparison for cycle generation, can be utilized to generate cycles for other cities and vehicle types.; The best SF cycle developed in this research is a 627-second speed and grade vs. time trace, with average speed 10.6 mph, average upgrade 3.6% and average downgrade 2.4%. By comparison with all the collected data and other existing bus driving cycles, I conclude that the new SF cycle with grade is better representative of the transit buses operating in SF.; ADVISOR results show that the grade sensitive SF cycle produces 11% more NOx emissions, about 5% more HC and CO emissions with 3% lower fuel economy compared to the same cycle without grade effect consideration. Due to the bus filter, the PM emissions are low that the effect of grade is not significant. The comparison of the diesel bus with trap with hybrid buses shows that the hybrid buses have better fuel economy on hilly roads while the diesel buses have lower NOx emissions compared to the hybrid buses. This study will provide valuable information to the city of SF with respect to future policy decisions on what kinds of buses best fit SF with consideration of both emissions and fuel economy.