Fuel and emission impacts of heavy hybrid vehicles.

Hybrid powertrains for certain heavy vehicles may improve fuel economy and reduce emissions. Of particular interest are commercial vehicles, typically in Classes 3-6, that travel in urban areas. Hybrid strategies and associated energy/emissions benefits for these classes of vehicles could be significantly different from those for passenger cars. A preliminary analysis has been conducted to investigate the energy and emissions performance of Class 3 and 6 medium-duty trucks and Class 6 school buses under eight different test cycles. Three elements are associated with this analysis: (1) establish baseline fuel consumption and emission scenario's from selected, representative baseline vehicles and driving schedules; (2) identify sources of energy inefficiency from baseline technology vehicles; and (3) assess maximum and practical potentials for energy savings and emissions reductions associated with heavy vehicle hybridization under real-world driving conditions. Our analysis excludes efficiency gains associated with such other measures as vehicle weight reduction and air resistance reduction, because such measures would also benefit conventional technology vehicles. Our research indicates that fuel economy and emission benefits of hybridization can be very sensitive to different test cycles. We conclude that, on the basis of present-day technology, the potential fuel economy gains average about 60-75% for Class 3 medium-duty trucks and 35% for Class 6 school buses. The fuel economy gains can be higher in the future, as hybrid technology continues to improve. The practical emissions reduction potentials associated with vehicle hybridization are significant as well