What is a hybrid bus?
Hybrid bus motors act like generators. Through a process called "regenerative braking", energy created while a bus slows or stops is converted to stored electric energy. Forty percent of the energy to accelerate the bus is actually energy saved during the braking process.
In 2007, the Duluth Transit Authority began operating two 35-foot hybrid electric buses. The hybrid electric buses are powered by diesel / hybrid electrical propulsion systems. This system reduces emissions and conserves fuel. Hybrid electric buses have enhanced acceleration, as they use electric power exclusively until they reach 10 mph. Hybrid buses run smoother and are quieter than conventional buses. Hybrid buses utilize a regenerative braking system that charges large Nickel Metal Hydride batteries whenever the buses are coasting or braking.
The DTA uses ultra-low sulfur diesel fuel (clean-diesel) with a soy-based blend in all its buses. During the winter months, the DTA uses the state mandated 2% soy-based bio-diesel fuel. During the non-winter months, the DTA uses a 5% bio-diesel blend and will increase the percentage to 20% blend when the fuel becomes available locally.
Hybrid buses are equipped with these features:
- Equipped with 5.9 liter 6-cylinder, clean-burning diesel engine
- Fuel economy is 33% better than standard buses
- Hybrids – 5.6 mpg;
- Standard Buses - 4.2 mpg
- Hybrid buses produce 90% fewer emissions than the buses they replace
- Hybrid electrical propulsion system reduce oxides of nitrogen emissions by up to 50%
- Transmission blends propulsion using two electric motors - one for electric power and one for mechanical
- Nickel Metal Hydride batteries are non-hazardous, maintenance-free and have a 6-year life
These vehicles are used for twelve years and cost about $188,000 more than a conventional diesel bus. The savings in fuel and maintenance make up for the cost difference.
DTA buses burn ultra low sulfur and soy-based diesel fuel:
- In compliance with EPA (Environmental Protection Agency) regulations for all diesel-burning engines, the clean-diesel engines in the Hybrid Electric Buses are designed to burn Ultra Low Sulfur Diesel Fuel.
- These clean-diesel buses also require using special motor oil (CJ-4) that captures more pollutants and reduces engine temperatures. The DTA currently uses this high grade oil in all its buses.
- The DTA has been using "Ultra Low Sulfur Diesel Fuel" in all buses for several years.
- The DTA uses a 2 percent bio-diesel blend of fuel during the winter months and a 5 percent bio-diesel blend during non-winter months. When a higher blend of bio-diesel fuel becomes available locally, the DTA will be able to increase its bio-diesel blend up to 20 percent during non-winter months. Currently, the State of Minnesota requires a 2 percent bio-diesel blend for use in all diesel engines.