ANCHORAGE, Alaska – For years, visitors wanting to see Denali National Park's grizzly bears, moose, sheep and caribou have had to ride school buses that polluted the air and spoiled the tranquillity with their noisy, carbon dioxide-spewing diesel engines.

Now park officials are testing a hybrid bus that promises to run cleaner, cheaper, and quieter.

The 230-horsepower hybrid bus – white and sporting pictures of Denali on its sides – went on a drive in the park Thursday. The plan is to test it this summer to determine its potential for replacing the park's 110 diesel buses.

Park managers do not allow visitors to drive their personal cars the length of the park road. Visitors board the buses near the park entrance. The 92-mile road, much of it unpaved, is the only way in and out of the nearly 6 million-acre park, home to Mount McKinley, at 20,320 feet the tallest mountain in North America.

The hybrid – looking a lot like a spiffy school bus – comes with a diesel engine but also has a hybrid system, said Keith Kladder, marketing manager for IC Bus of Warrenville, Ill., the manufacturer of the bus.

Production of the hybrid buses began about a year ago, Kladder said.

“The technology is just coming to market,” he said.

The diesel buses emit carbon dioxide, nitrogen oxide and particulates. The hybrids are cleaner, reducing carbon dioxide emissions by as much as 40 percent, nitrogen oxide by up to 20 percent and particulate matter by as much as 30 percent, according to IC Bus.

Diesel buses also are expensive to operate – not a small issue, considering that diesel fuel in the Denali area costs more than $5 a gallon.

When Doyon/Aramark, the concessioner responsible for transportation inside the park, got the park contract in 2003, it was challenged to look at new technology, including hybrids.

The hybrid system used on the bus was developed by Enova Systems, based in Torrance, Calif. It couples a diesel engine with an 80-kilowatt powertrain that incorporates a transmission, batteries and an electric motor.

The system gathers energy when the brakes are used. The batteries are charged while the bus is slowing down. That, in turn, provides additional power for acceleration, allowing the diesel engine to mostly idle while the bus increases speed.

The hybrid bus requires as much as 70 percent less fuel.

“The beauty is when you use less fuel, you emit fewer pollutants,” Kladder said.

The hybrid application is perfect for park buses, because just like school buses, they make a lot of stops and starts, Kladder said.

If the hybrid test is a success, the park will look at replacing its diesel buses with hybrids as needed. Two to 12 buses are replaced each year. Buses in service can't be more than 10 years old.

A typical hybrid bus costs about $200,000, or twice that of the average bus, Kladder said. In time, he said, the company hopes to bring the cost down with increased production.

For park managers, it's not all about money. The quieter hybrid motors will enhance the visitor experience.

One big problem with the diesel-engine buses – which drive an average of 1.2 million miles per year – is that they are noisy. They can be heard from afar in the park.

The hybrids are quiet.

“Can you imagine the thrill of moving slowly and silently past a bear nursing its cub or wolf hunting along the road?” said Elwood Lynn, assistant superintendent of operations for Denali.

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