A hybrid car has a battery-fed electric motor providing boost for the small gasoline engine when accelerating. Same thing with these $500,000 Orion VII buses, by DaimlerChrysler Commercial Buses. The primary powerplant is a 5.9-liter, 270-hp reduced-emissions Cummins diesel engine, not much different from the one in a Dodge Ram pickup truck, except the bus weighs 42,540 pounds fully loaded (with 44 passengers and 100 gallons of diesel fuel), the pickup just 6,350 pounds. (A traditional non-hybrid bus engine would be twice the displacement.)


The diesel engine has been optimized to run at near-constant speed and dumps its power to the array of 46 batteries on the roof. The batteries provide additional power for quick starts and hill climbs (it's not the Alps, but New York has a few slopes). The hybrid bus has no transmission and no direct connection between the diesel engine and the wheels. Instead, like a diesel locomotive, the Orion VII diesel engine turns a generator, which runs through a control unit developed by BAE Systems, which drives an electric motor that powers the bus. The controller also sends and receives power from the battery array. Acceleration is both faster and smoother. The other passenger-pleasing feature is the low floor, just 14.5 inches off the roadway, 11 inches when the suspension kneels.

At the late fall rollout, New York City transit officials got overenthusiastic, and at one point -- illustrating the danger of setting politicians loose with statistics -- Transit Authority president Laurence Reuter said a bus was the equal of 15,000 Priuses. Translation: New York City has a fleet of 325 hybrid buses recently delivered, with 500 more on the way through 2007. When all 825 are in service, together they'll have the same savings in fuel consumption and reduced emissions as replacing 15,000 passenger cars with hybrid cars such as the Toyota Prius. In other words, one hybrid bus can be as earth friendly as 18 to 20 hybrid cars.

Including compressed natural gas (CNG) buses, more than a quarter of New York's 4,500 buses will be reduced-emission vehicles. Compared with low-emissions diesel transit buses and CNG buses, the hybrids emit less than half the nitrous oxides (NOx) and one-fourth the carbon monoxide (less than one-tenth the CO of a CNG bus). Chugging along New York City streets at an average of less than 4 mph and getting 3.6 mpg, each hybrid will save 5,000 gallons of diesel fuel a year.


The technology doesn't come cheap. The Orion VII hybrid bus costs about 30 percent more than a diesel-powered transit bus. Andreas Renschler, DaimlerChrysler's board-of-management member in charge of commercial vehicles, says that much of the cost differential will be recaptured over the decade or more the bus is in service: less fuel consumed, no transmissions to overhaul, and fewer brake pads to replace. But on a purely financial basis, the hybrid may not earn back its higher cost. The intangible is the value of cleaner air. Unfortunately, because of the high up-front costs, so far there have been few takers for hybrid buses in the world's most polluted cities, such as Mexico City, Bangkok, Beijing, or Shanghai, although many are adopting CNG buses.