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The greening of the city bus

The bus has never been a glamorous way to get around, but it is becoming a showcase for energy efficiency. Photos: Green buses for San Francisco

In the world of hybrid cars and alternative energy, the municipal bus has become the vehicle to watch.

Short driving distances and the stop-start nature of urban driving have made buses into something of a test platform for ideas for energy-efficient vehicles. Major cities have begun to buy into these buses as well.

San Francisco, for instance, announced this week that it has ordered 56 Orion VII hybrid diesel vehicles from DaimlerChrysler and will have 86 of the buses, which run on diesel and battery power, on the city's roads by 2007.

New York, meanwhile, already owns several Orion VIIs and has plans to put 1,000 of them on the streets by the end of the year, according to Andreas Renschler, a member of the board of DaimlerChrysler. Toronto has ordered 200.

Daimler also has kicked off a trial in California with the Sprinter, a plug-in hybrid delivery vehicle. Plug-in hybrids run almost exclusively on electricity and get recharged at night by being plugged into a wall socket. The batteries can take up a substantial amount of space in these cars, but they get far better gas mileage than standard light trucks or other hybrids.

The company is also participating in trials for hydrogen buses in China and 30 cities in Europe.

Why buses? The nature of the tasks they perform fits well with a lot of these technologies. Standard hybrid cars get recharged when the brakes are applied in a process called regenerative braking. (The mechanical energy of the car is converted to electricity). Drivers hit the brakes in cities a lot, but far less so on the freeway.

Urban buses also don't get cranked up to top speeds, so the electrical engine can perform more of the work of propelling it forward.

Orion VII gallery

"For long-mileage driving, a hybrid is not the right thing. If you drove from San Francisco to New York, you'd lose all of the benefits of a hybrid," Renschler said. "But for stop-and-go, it is the perfect solution."

Similarly, hydrogen dovetails well with bus driving. Because buses generally don't go long distances, drivers don't have to worry about being stranded miles away from a hydrogen filling station: One can be built close to the bus routes. The fact that hydrogen vehicles sometimes top out at 90 miles an hour isn't a problem with buses, which typically lumber along at 30 miles per hour or less.

Daimler actually put a hydrogen bus on the streets of Stuttgart, Germany, in 1969, said a company representative. "It worked well, but there was no interest because gas prices were low."

San Francisco Mayor Gavin Newsom said the city conducted a study from 2001 to 2003 and examined several types of energy-efficient buses before placing the orders for the Orion diesel hybrids. Buses that run on compressed natural gas, used in some cities, wouldn't work well in hilly San Francisco, he said.

The city is also looking at biodiesel-powered and fuel cell buses.

"Our goal is to be 100 percent emission-free in municipal transportation by 2020," Newsom said.

From a rider's perspective, the Orion VII isn't much different than a standard bus. It comes with somewhat fewer seats, but doesn't make nearly as much noise. It emits a humming sound, rather like a large meat refrigerator.

Right now, energy efficiency isn't cheap. The Orion VII buses cost around $488,000 apiece. A standard diesel bus might cost $250,000 to $280,000, according to the Daimler representative. The Orion VII gets about 4.5 miles to the gallon--that's not much compared with a Toyota Prius, but standard buses get only about 3.5 miles per gallon.

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Video: A greener ride home
Diesel-electric hybrid buses headed to the streets of San Francisco.

In other words, the Orions represent about a 35 percent improvement in fuel economy. Over a 12-year period, these buses will use 1.2 million fewer gallons of diesel than a standard bus, Renschler said. That's about 13,000 U.S. barrels of oils. Early results in New York City also indicate that the buses may require less maintenance.

The buses also reduce the particulates spewing out of the tailpipe by about 90 percent. Nitrogen/oxygen compounds are reduced by about 40 percent, and greenhouse gases overall are reduced by about 30 percent.

Oil companies and car manufacturers are further looking at ways to reduce particulate matter by adopting cleaner forms of diesel made out of natural gas.

For consumers and for distance driving, DaimlerChrysler is touting its BlueTech diesel engines, which burn cleaner than standard diesels. The company already sells cars with these engines in Europe and will bring a Mercedes to the U.S. in the fall with one.