The long-delayed State Route 509 extension may be scaled back because of escalating costs.

Earlier estimates pegged the project's cost at $1.03 billion.

New projections now place the final bill at $1.35 billion-a 31 percent increase.

The original plan called for six lanes extending from South 188th Street, where the freeway now ends, to Interstate 5 near South 200th Street.

A new south access road from Sea-Tac International Airport to SR 509 would be included in the project.

Two of the six freeway lanes would be reserved for high occupancy vehicles (HOV).

Three lanes would run seven miles along Interstate 5 from South 200th to South 320th Street in Federal Way.

A more modest alternative would eliminate the two HOV lanes and improvements to I-5.

What eventually gets built is in the hands of the committee putting together a regional transportation ballot measure, according to Paul Johnson, SR-509 project engineer.

Then the voters will make the final decision.

Council members from King, Pierce and Snohomish counties serve on the Regional Transportation Investment District committee.

Their ballot proposal, covering major transportation project, is scheduled to be ready in April and go before the voters in the fall.

If passed, tax increases for the average household would be about $100 per year.

A companion measure to fund Sound Transit rail projects would also be considered by voters.

Both measures would have to pass or they would jointly fail.

Johnson said the cost of the proposed project has inflated because prices for concrete, steel, fuel and labor have all skyrocketed.

"The project includes lots of bridges so we would need a lot of concrete," he added.

With massive projects underway worldwide including the rebuilding of the hurricane-damaged Gulf Coast, there is stiff competition for materials and workers.

"We are quite a ways along on the project," Johnson noted.

Last summer, a wetlands mitigation site at South 188th Street and Des Moines Memorial Drive was built.

Funds budgeted from the 2005 state gasoline tax increase provided $30 million for property acquisition, design work and environmental permit applications.

The project has about $133 million in total funds available-far short of the over $1 billion needed.

Transportation planners say the SR 509 extension along with a new Alaskan Way viaduct or tunnel will serve as a critical north-south alternative to I-5 through Seattle and south King County.

They cite several expected improvements:

Congestion through downtown Seattle and the Southcenter hill will be reduced, making the roads faster and safer.

Freight will move more smoothly between marine ports and the industrial areas of Seattle and South County.

The airport will connect directly to I-5 from the south.