Public transportation in Ann Arbor is about to become even more environmentally friendly.

Ann Arbor Mayor John Hieftje recently unveiled plans to curb the amount of fossil fuels used by the city's buses.

As part of "The Mayor's Green Energy Plan," the Ann Arbor Transportation Authority plans to replace all its buses with a "green fleet" of hybrid buses within three years.

But while Ann Arbor plans to use city funds and outside grants to buy 15 hybrid buses by November, the University has no plan to introduce hybrid technology to its own buses.

Although the hybrid buses use about 30 percent less fuel than the ones used now, they cost about 83 percent more, AATA maintenance manager Terry Black said.

Keith Johnson, the general manager of the University's Fleet and Garage Operations, said that because the hybrid buses cost so much more than regular ones - $550,000 versus $300,000 - the University will hold off on buying hybrid buses for now.

But Johnson said the University plans to reinvestigate hybrids in 10 to 12 years when higher fuel costs and lower prices of hybrid technology make the transition a more cost-effective option.

Replacing every bus in the AATA's 75-bus fleet with hybrids, which Hieftje has pledged to do over the next three years, will require a hefty initial investment, but Black said he expects the city to see more than just a return in environmental well being. Over the next 12 years, Black said the AATA expects to save $2,500,000 in fuel and maintenance costs as a result of introducing the hybrids.

Johnson said the financial benefit would not be as great for the University because its buses typically only rack up half the mileage of city buses.

"It's just more attractive to them," he said.

Hybrid technology is especially beneficial for vehicles that encounter frequent stop-and-go traffic, like buses. Hybrid buses are mostly powered by fuel combustion, but are assisted by electrical energy. When the bus's brakes are applied, a generator converts the energy released from deceleration into electrical energy, which is stored in a battery and used when the bus accelerates.

Although the University hasn't adopted hybrid technology, it has been making significant efforts to be eco-friendly, Johnson said.

"Based on a recent conference with our peers in the Big Ten, we're in the forefront," he said.

The University's transportation department updated many vehicles to run on bio-diesel fuel in 2000 to reduce fossil fuel consumption and greenhouse emissions.

Bio-diesel fuels are often made from plant products. While they are carbon based and release pollutants when burned, government studies have shown bio-diesel to be less harmful to the environment than petroleum-based fuels.

When the University updated its buses in 2000, the option of retrofitting regular buses to run on bio-diesel cost the University $11,000 per bus - much less than investing in newly developed hybrid bus technology.

"Bio-diesel was one area where we could make the switch fairly seamlessly," Johnson said.

The University has avoided using nearly 390,000 gallons of fossil-based diesel fuel since it switched to bio-diesel.

By the Numbers

$550,000: The cost of a hybrid bus

$300,000: The cost of the model of bus the University uses.