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The Chevrolet Tahoe Hybrid's bank of nickel-metal hydride (NiMH) batteries, located out of the way and under the second row of seats, forms the heart of the truck's Energy Storage System. Photos: General Motors Corp.
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Because the Chevrolet Silverado pickup truck has the same general configuration and dimensions as conventional vehicles — but boasts better fuel economy both in city and highway driving — it makes an ideal choice for fleet managers.

If it doesn't already, your fleet soon will include hybrid trucks. Given high fuel prices, concern for the environment, and the goodwill generated by setting an example for your community, it's inevitable.

The EPA's Smartway program rewards both public and private owners of fuel-efficient, less-polluting vehicles. Also, in a growing number of cities hybrids can use high occupant vehicle (HOV) lanes on expressways.

Financial incentives like development grants make it easier for governments to afford higher-priced new technologies. And thanks to diesel prices of $4.50+/gallon, payback on the greater initial investment is shorter than ever.

TWO TYPES OF HYBRIDS

Just as corn is bred to provide the best characteristics of each parent strain — yield/acre and pest resistance, for example — a hybrid vehicle combines two technologies to get each one's advantages.

Gasoline-electric is most common, combining the internal combustion engine's power with the electric motor's energy efficiency and emissions-free operation.

But for commercial applications, diesel is more energy-efficient. Diesel-hydraulic hybrids are being developed for frequent stop-and-go driving; instead of using only service brakes to slow and stop, the trucks convert their kinetic energy into hydraulic pressure stored in a tank. Pressure is released to turn hydraulic motors to assist acceleration, relieving the burden on the engine and reusing energy normally lost as heat from the brakes.

All hybrid systems combine power sources for acceleration and use hydraulic or electric motors for regenerative braking. The reuse of braking force is why hybrid vehicles of all sizes and types often get better fuel economy in cities than on highways.

General Motors' full-size hybrid pickups, the Silverado and Sierra, and the SUVs built on the same platforms, the Tahoe and Yukon, get similar city and highway mileage, according to EPA estimates. They have the same general configuration and dimensions as the conventional models, but towing capacity and payload are reduced, most likely to avoid overstressing the electric motor.

I recently drove a Chevrolet Tahoe Hybrid with a 6.0-liter V-8 gasoline engine that produces a healthy 332 hp and 367 foot-pounds of torque. At part throttle, the engine handles the 5,617-pound (dry) vehicle plus payload with ease.

Nickel-metalhydride (NiMH) batteries form the heart of the Energy Storage System, which contains batteries and a logic unit that directs 300 V to power the vehicle, 42 V to the electric power steering system, and 12 V for the vehicle battery and electrical accessories.