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 tranquility with their noisy, carbon dioxide-spewing diesel engines.

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

The 230-horse power hybrid bus _ white and sporting scenic views of Denali on its sides _ went on an actual drive in the park Thursday. The plan is to test the hybrid 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 on 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 particulate matter into the air. The hybrids are cleaner, reducing carbon dioxide emissions by up to 40 percent, nitrogen oxide by up to 20 percent and particulate matter by up to 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 needs up to 70 percent less fuel.

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

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

If the hybrid test is a success, the park will look at replacing its diesel buses with hybrids as needed. From 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 a long ways off 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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On the Web:

http://www.icbus.com

http://www.nps.gov/dena/