Abstract
This study investigates life-cycle greenhouse gas (GHG) emissions in different bus technologies with a Public Transit Greenhouse Gas Emissions Management Calculator (hereafter the Calculator) and selected driving schedules at Knoxville, TN area. A range of methodologies to estimate GHG emissions from various categories of transit agency activities have been integrated into the Calculator which has been funded by the Federal Transit Administration. To estimate the direct emissions, a method with the operating mode bins, based on scaled tractive power, of MOVES has been implemented in the Calculator. Parameters including driving schedule, road grade, and passenger load, were specified for the estimation. Load-based life-cycle GHG emissions with five predefined driving cycles in eight combinations of powertrain and fuel types, including conventional diesel bus, CNG bus, parallel and series hybrid buses, battery bus, fuel cell bus, plug-in fuel cell bus and plug-in hybrid bus, were compared and the results show that driving schedules have impacts on the estimated emissions. In comparison to findings from other studies, the selected Knoxville Area Transit (KAT) driving schedules are estimated to have lower CO2 equivalent emissions with hybrid technology and higher emissions with the conventional diesel, CNG, and fuel cell technologies. Sensitivity analysis of passenger loading parameter with different bus technologies and driving schedules has been demonstrated. Findings and recommendations include (1) transit agencies have better to conduct the evaluation with their own local conditions; (2) battery bus has the lowest emissions in most of the scenarios investigated; (3) the mass of CO2 equivalent emissions per mile is a good indication for the evaluation; (4) route length does not matter in the analysis; (5) the passenger loading parameter affects the emissions in bus technologies differently.