Braking for Fuel
School buses are known for belching black smoke as they chug along their routes, burning fuel at about seven miles per gallon. But two Texas school districts have joined a nationwide buyers' consortium of 15 school districts and school bus purchasers to improve air quality and save fuel.
The consortium plans to purchase 19 plug-in hybrid electric buses (HEBs), the first of their kind in the U.S., said Ewan Pritchard, hybrid program manager and engineer for Advanced Energy, a North Carolina-based nonprofit organization that promotes innovative approaches to energy. Austin Independent School District (AISD) and Killeen Independent School District (KISD) each plan to purchase one bus, Pritchard said.
A traditional diesel school bus emits more than 500 tons of air pollution and consumes 20,700 gallons of fuel over its 15-year lifetime, according to Advanced Energy. Kids riding traditional buses are exposed to these pollutants during their commute, especially when the buses idle to pick up passengers, Pritchard said.
"Students are right at the height of the tailpipe," he said.
Particulate matter (PM) from diesel engines can cause respiratory problems such as asthma, and the medical community has linked PM with illnesses including lung cancer and heart disease, according to Advanced Energy's Hybrid Electric School Bus Feasibility Study.
Plug-in HEBs greatly reduce tailpipe emissions and eliminate them completely when buses are idling, Pritchard said.
Instead of using up energy when a bus slows or stops, a battery recaptures that energy and recharges itself. And unlike conventional hybrids that only recapture energy when slowing down, plug-in hybrids also recharge at night by plugging into the power grid when electricity is cheapest and when power plants produce less pollution, Pritchard said.
"People automatically assume we haven't included the power plant emissions [into our emissions estimate], which we have," Pritchard said. "One of the things we're pushing people to do is recharge them with green power, then there are no emissions from electricity."
Less over a lifetime
Although plug-in HEBs cost more than their diesel counterparts--about $215,000 a bus compared to about $70,000 for a traditional bus--Advanced Energy estimates the HEB will pay for itself in fuel savings over its lifetime.
"Our business study was based on $1.40 per gallon," Pritchard said. "Everything indicates that the savings would be much better now that fuel prices have increased."
Diesel fuel averaged $2.95 per gallon in August 2006, according to the Energy Information Administration. Because an HEB's battery engages for much of its route, fuel economy nearly doubles, from 7.6 miles per gallon with a regular school bus to 12.7 miles per gallon with a plug-in HEB, Pritchard said.
With a fuel budget of $2 million a year, AISD could use the savings, said Kris Hafezi, AISD assistant director of transportation.
AISD hopes to receive its plug-in HEB by July 2007, said Andy Welch, director of communications for AISD. The district will receive a $65,000 grant from Austin Energy as well as federal funding to help pay for the bus, Welch said.
KISD, however, is about $70,000 short of fully funding its HEB purchase, said KISD Transportation Director Joe Hart.
"We'd be interested in using those buses in our fleet not only as a reduction in pollution, but also as a fuel savings measure," Hart said. "The estimated mileage on the plug-in HEB is about twice what we see right now, so depending on how many we had in the fleet, there would be an offsetting amount in the cost of fuel."
The district spends $36,000 to $40,000 a week on fuel for its fleet of 250 buses, Hart said.
"This is the only technology that can reduce your emissions and decrease your operating costs, so it provides a benefit to society and a benefit to school systems," Pritchard said.