Rapid Shift to Fuel-Saving Hybrid Buses Is Reportedly Underway in United States
By Scott Doggett December 1, 2008
In Troy, Michigan, engineers are reportedly tweaking what they believe to be the public transit vehicle of the future: a super-lightweight hybrid bus.
The GTB-40 (right) is made of a high-strength steel that will last longer than most bus frames. Its builder, Fisher Coachworks, says the chassis allows it to zip along with half the weight of its peers.
And, its hybrid-electric engine not only consumes less fuel, but also stores electric energy whenever a driver hits the brakes.
The result is a bus that gets 10 miles per gallon--if you convert its battery power to diesel equivalents, that is.
But the average diesel bus--the dominant vehicle in public transit--gets just over 3 miles to the gallon, so the new mpg number has city transit agencies taking note, the subscription news service ClimateWire reported today. Battered by fuel prices and hoping to spruce up their environmental records, they are buying more and more hybrid buses to run everyday routes.
Compared to the tens of thousands of diesel buses already in service, the hybrids are few. In most places, they haven't graduated from pilot projects. But they're at the front of a trend that's been building since early this decade. In 1995, according to the American Public Transportation Association, only 6 percent of buses ran on anything other than straight diesel or gasoline. In 2007, that number had risen to 22 percent, ClimateWire reported.
"They're all prototypes. None are really final in the sense that they're out on the road in any type of mass," Lurae Stuart, an alternative-fuels analyst with the American Public Transportation Association, told ClimateWire. "But that's still a rapid change for a technology."
The new buses use a range of technologies, from natural-gas engines to fuel cells and biodiesel. Leading the way are diesel hybrids, which now make up one of every five buses being built, according to Stuart.
Half a Million Bucks
The hybrids don't come cheap--they cost about $500,000, compared to roughly $300,000 for a diesel--but some cities are beginning to appreciate their bottom line.
"Today, with rising fuel costs, there's now an economic base," Josh Goldman, an engineer with Golden, Colorado-based bus developer Proterra, told ClimateWire. A bus designed to travel 500,000 miles in its lifetime could cost more than half a million dollars in fuel, he said. A hybrid engine could cut that bill by several hundred thousand dollars.
And since most cities pay for only a fraction of the bus itself--the Federal Transit Administration offers 80 percent federal funding for capital costs--the bus pays for itself even more quickly.
That's the idea in New York City, whose 825 hybrid buses constitute the largest fleet in the country. Gary Labouff, research director at New York City Transit, said the city paid about $500,000 apiece for the buses. They have gradually accumulated since the city piloted hybrids in 1996, so they mostly use the lead-acid batteries found in the oldest hybrids.
Stop and Save
But even these first-generation hybrids pack a wallop: Labouff estimated that their fuel economy is 25-30 percent better than that of diesel buses. The biggest benefits come from stop-and-go routes, on which buses speed up to about 10 miles per hour, only to screech to a halt at the next block: The regenerative braking system uses every hard brake to spin the generator to make juice for the next stretch. Since this system takes pressure off the brakes, it lowers the maintenance costs of the bus.
The city's fleet will begin a transition when its new order of 850 hybrid buses arrives in coming years. These buses will use the more modern lithium-ion battery technology, which is lighter and is better at holding a charge.
These batteries, experts said, are the key to cutting hybrids' costs and putting them on an even footing with their low-mileage diesel counterparts.
"The weak link right now is the energy storage piece," Stuart, the APTA analyst, told ClimateWire. With the country's first wave of hybrids only four to six years old, no one knows just how quickly these batteries will wear out.
Just as in light-duty cars, researchers are hoping to develop a battery that is light, able to hold a charge, and long-lasting. But the bar is higher for heavy vehicles, which put on more miles than cars and need a battery that can withstand more frequent charges and discharges.
10-Minute Recharge
As cities explore the use of hybrid buses in their fleets, a handful of companies is searching for the technical solutions that can make future hybrids even better.
Goldman's Proterra, for example, is designing a plug-in hybrid bus that can run up to 50 miles on pure battery power and recharge in 10 minutes, just long enough for a driver to take a break or switch out.
And Capstone, a company based in Southern California, is working with an Energy Department laboratory to develop a bus that runs on microturbines. These mini-generators, which run on natural gas, will recover most of the heat from combustion, charging the battery that propels the bus.
Priced at $1 million or more, these advanced buses can't compete in the marketplace yet. But with the nation's diesel-bus fleet just hitting its prime, researchers may have some time to get costs down. The average bus in America is about 8 years old, according to APTA--four years less than the 12-year period FTA requires that federally funded buses run.
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More than triple the fuel economy? Not bad. Granted, it's just a concept, so if it only ends up getting double the fuel economy, that's still quite an improvement.
Have they trialed natural-gas hybrids too?
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