SEATTLE --- King County in Washington is using Kenworth Truck Company's medium-duty, hybrid-electric truck for utility operations.

"King County has taken a leadership role in adopting new technologies that can reduce fuel consumption and greenhouse gas emissions," said Harold Taniguchi, director of the King County Department of Transportation. "We’re pleased that the county's new Kenworth medium-duty hybrid is exceeding our expectations in fuel economy, performance and driver acceptance."

Located in the greater Seattle metropolitan area, King County covers more than 2,100 square miles and is the nation's 13th most populous county. The King County Department of Transportation, which became the first government agency to place the new Kenworth hybrid into service, uses its new Kenworth Class 7 hybrid to maintain traffic signals. The hybrid is equipped with a utility bucket atop a 50-foot boom, which is longer than a standard aerial lift. While a non-hybrid utility truck must idle to operate its lift, the hybrid's lift typically operates on electric power, which reduces emissions.

"We’ve logged a little over 5,000 miles as of the first of this year, and the Kenworth hybrid has already achieved a 25-percent reduction in fuel  consumption over a comparably equipped conventional model," said King County Fleet Administration Division Director Windell Mitchell, who expects to attain a 30-percent or more improvement in fuel economy as the truck is further broken in by the county.

The need to refuel less often allows crews to remain in the field for longer time periods, which is especially important when 12-hour shifts are  required during storms and other emergencies. "Employees can travel farther and get a lot more work done without having to make return trips to the county's fueling station or purchase higher priced fuel at a retail location," said Mitchell.

The county uses B-20 biodiesel as its fuel. The blend of 20 percent  biodiesel and 80 percent ultra lowsulfur diesel provides additional reductions in greenhouse gas emissions, which is especially important for King County. In 2006, it became the first county with a large transit fleet in the United States to join the Chicago Climate Exchange, where members buy and sell "carbon credits." By joining, the county made a legally binding commitment to reduce its emissions of carbon dioxide and other climate-altering greenhouse gases each year.

Drivers also have helped make the Kenworth hybrid a valued part of the county's fleet. "Our drivers really like the Kenworth hybrid," said Fleet Equipment Manager Bob Toppen. "I’ve driven it myself, and it has a great fit and finish inside and out. It's a quality truck. The PACCAR PX-6 engine provides good power and acceleration, and even when the engine is running, you can barely hear or feel it."

Kenworth’s medium-duty hybrid, which can carry a payload of up to 16,000 pounds, features an integral transmission-mounted motor/generator, frame-mounted 340-volt battery, and dedicated power management system. Above 30 mph, the Kenworth hybrid operates like a standard diesel vehicle with all power coming from the engine during steady driving conditions. Below 30 mph, it uses a combination of diesel and electricity with the system automatically switching between the two modes of operation. Electricity generated through regenerative braking is stored and used for acceleration, assisting the diesel engine.

Kenworth plans to begin full-scale production of its medium duty hybrid in 2008.