A public transportation service in Minnesota’s Twin Cities is using hybrid buses to reduce energy use and greenhouse gas emissions.
The Minneapolis-St. Paul region’s Metro Mobility, which provides transit services to riders with disabilities, was scheduled to replace 35 small diesel buses. Each of the buses, on Ford E-350 chassis, had operated 225,000 miles or more. Using $1.1 million in TIGGER funds, Metro Mobility replaced 15 of the 35 buses with gasoline-electric hybrid buses integrated on Ford E-450 chassis.
The new gasoline-electric hybrid buses, which began operating in November 2009, are 10%–20% more fuel efficient than conventional gasoline buses. Their propulsion system, manufactured by Azure Dynamics Corporation, has a parallel hybrid configuration: the gasoline engine has a mechanical connection to the electric motor, which also functions as a generator to power electrical systems on the vehicle. The parallel hybrid system architecture is E85-compatible and anti-idle compliant. In addition to reducing fuel consumption, the hybrid system’s regenerative braking reduces brake wear and maintenance by 75%. Engine run time and maintenance are reduced by about 25%.
As an additional component of the TIGGER project, Metro Mobility purchased a conventional gasoline bus retrofitted with an Eaton hydraulic launch-assist (HLA) system, as part of a field test for the HLA technology. Eaton financed, installed, and maintains the HLA system, while Metro Mobility operates the vehicle in service as a pilot project to collect realworld operations data. During vehicle deceleration, the HLA system captures energy that would otherwise be lost to friction and heat, and stores it in a hydraulic accumulator filled with nitrogen gas. The energy is then returned to the vehicle drive train during subsequent acceleration, thereby reducing the amount of work required from the internal combustion engine. The HLA system is especially well suited to reduce fuel consumption in Metro Mobility’s repetitive stop-and-go drive profiles.