Holland America Line Westours Inc. has four luxury double-decker dome cars under construction that the company and the manufacturer say will be the largest and longest passenger cars ever built.

The cars, slated for service next spring in Alaska, are 89 feet long, about 4 feet longer than any competitor's, said Dave Beagle, Holland America's vice president of transportation in Seattle.

"We believe we're setting a new standard," said Beagle.

The four cars cost $3 million apiece and are being built by Colorado Railcar Manufacturing LLC of Ft. Lupton, Colo.

"These are the most luxurious rail cars built in the world," said Tom Janaky, Colorado Railcar's vice president of sales and marketing. "Holland America wants to be bigger and better."

Holland America's McKinley Explorer carries passengers between Anchorage and Fairbanks, stopping in Denali National Park. The service runs between May and September each year.

Two other tour companies and the Alaska Railroad Corp. haul passengers on summertime trips. The state-owned railroad's engines often pull all of the companies' cars -- and its own -- on a single train.

Holland America is banking on the bigger, newer cars bringing more business.

"One needs to be competitive because it is a competitive situation in Alaska. I believe these will make a difference," Beagle said.

The cars feature full dining room and kitchens, a lounge, viewing platforms, and seating for 88 people, Beagle said. The new cars also have elevators, allowing easy access to the upper dome deck for wheelchair-users, Beagle said.

The cars will have slanted windows on the ends of its dome cars, unlike its competitors. Beagle said the company didn't want the "bread box" or "brick" look of the other passenger dome cars.

Each car will feature Alaska Native paintings and carvings, and wool seats and carpets made from Swiss sheep, Beagle said.

The cars are 18 feet, 1 inch high, the maximum allowable by the Alaska Railroad Corp. Beagle said engineers found that the 89-foot length was "the maximum logical dimension."

There won't be any longer luxury domes in Alaska, Beagle said.

"This is it," said Beagle.

The 88-passenger cars seat 22 more folks than the tour company's existing fleet of 13 dome cars, two of which are being sold for $375,000 apiece to a Lower 48 railroad, Beagle said.

All passenger domes in Holland America's current fleet were built in the early 1950s, Beagle said.

He said the tour company has the largest fleet of dome cars in the world.

Ironically, Beagle said the old cars will probably still have a little better ride than the new cars under construction, since they have four more wheels and two more axles than the new domes. Companies haven't made the extra-wheeled cars for nearly 50 years, Beagle said.