The Austin Independent School District is one of a few school districts in the nation that use plug-in hybrid electric-diesel school buses.
The district began purchasing the fuel-efficient buses in 2006 and has purchased about 25 new low-emission buses each year since then.
The hybrid buses cost almost three times as much as diesel buses to buy new, but have a 40 percent higher fuel efficiency, according to the Alternative Fuels and Advanced Vehicles Data Center at the Department of Energy.
Record-high fuel prices are forcing school districts to re-evaluate their transportation budgets and experiment with alternative fuels.
State and federal rebates for school districts that switch to alternative fuels have popularized the trend of districts choosing to spend more money to buy low-emission school buses, according to Texas Railroad Commission officials.
On Monday, Northside Independent School District in San Antonio became the first school district in the country to purchase a fleet of brand new propane-fueled school buses. The school district received a $66,000 grant from the Texas Railroad Commission to reward its investment in the 16 low-emission buses.
Propane buses are between 87 and 99 percent cleaner burning than regular buses, which creates cleaner air, said Heather Ball, assistant director for marketing and public education at the Texas Railroad Commission.
Natural gas releases less carbon dioxide, but propane has a shorter lifespan in the atmosphere. The end result is that natural gas has a greater global warming effect than propane, according to a study conducted by the Propane Research and Education Council.
Austin's Capital Metro is researching several alternative fuels and will eventually replace a large portion of their fleet with low-emission buses, said Capital Metro spokeswoman Misty Whited.
Whited said public transit system authorities must take into consideration the longer time spans a city bus is on the road and the larger populations that utilize public transportation versus a school bus, when considering alternative fueling methods.
"There are pros and cons to every alternative," Whited said. "For example, a gallon of diesel produces more energy than a gallon of propane, so if we switched to propane we'd have to buy more of it and possibly limit passenger capacity. There are a lot of factors you have to weigh."
A 50-cent-per-gallon federal tax rebate for propane makes the fuel cheaper. Last year, the Northside School District saved $220,000 on the few older propane buses the district purchased.
Propane is the most widely used fuel alternative in the U.S., and there are currently 1,500 multifunctional propane buses in Texas, Ball said.
Other energy alternatives considered by transportation authorities around the state include biodiesel, electricity, hydrogen and ethanol.
According to the Department of Energy Web site, some of these alternatives are not practical because they are not established in commercialized fuel suppliers like gas stations, so they are not as accessible for easy refueling as gas.
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