The city is preparing to change the exits and double the width of the Spokane Street Viaduct in anticipation of heavier traffic during the upcoming years of construction to makeover another important elevated roadway, the Alaskan Way Viaduct downtown.

When driving out of West Seattle, motorists first cross the West Seattle Bridge. The Spokane Street Viaduct then carries traffic eastward to Interstate 5.

Interstate 5 will be the main detour route for the 110,000 vehicles per day that currently use the Alaskan Way Viaduct so the connectors must be improved ahead of time.

The timing for construction is up in the air. City officials want the expansion project completed before work starts on the Alaskan Way Viaduct. However, enough money to cut a tunnel to replace the waterfront viaduct is still in question. The Washington Legislature appropriated $2 billion but that's not enough to build a tunnel, the state's preferred option.

Even though the Spokane Street Viaduct is owned by the city of Seattle, expanding it will require the financial assistance of the state, King County, the Port of Seattle and the federal government in addition to the city, said Stuart Goldsmith, project manager for the Seattle Department of Transportation. Expansion of the Spokane Street Viaduct would cost $128 million to $145 million, he said. So far, the city of Seattle has secured only about $31 million for the project.

The pressing need to replace the Alaskan Way Viaduct might spur public officials to allocate money to widen the Spokane Street Viaduct first. Expansion of the Spokane Street Viaduct must start no later than late 2007 to be finished in time, Goldsmith said.

Currently the Spokane Street Viaduct is 45 feet wide with two lanes in each direction. The Seattle Department of Transportation wants to expand the road deck 41 feet farther north. The expanded viaduct would run between East Marginal Way and Sixth Avenue South. The change would widen the viaduct's narrow lanes, provide space for road shoulders and create a third lane for westbound vehicles to maneuver on and off.

The dangerous westbound exit at Fourth Avenue South is scheduled for demolition. Exits usually veer gently away from the thoroughfare, but the current Fourth Avenue exit is a sharp right angle that requires motorists to nearly stop to make the turn from a 35 mph elevated roadway with narrow lanes and no shoulders.

The new eastbound exit at Fourth Avenue South will loop to the right like a cloverleaf and take vehicles down to ground level. A traffic signal will get them onto Fourth Avenue with northbound traffic going under the viaduct to head downtown.

The new eastbound exit at Fourth Avenue could be a two-lane exit because the eastbound transit lane will end at Fourth Avenue, Goldsmith said. Although it is uncertain yet whether the transit lane might be turned into a high-occupancy vehicle lane.

There will be new on and off ramps at First Avenue South too.

The surface of the entire new width of the viaduct would be repaved with concrete

Spokane Street South at ground level is to be repaved too. Parts of it will get a new paved median.

The viaduct's expansion will create an outdoor ceiling over the sidewalk that runs along the north side of Spokane Street. The sidewalk itself will be broadened to accommodate bicyclists as well as pedestrians, Goldsmith said. It will connect to a bicycle path planned on Fifth Avenue.

If planners cannot secure enough money to do the project all at once, it might have to be built in phases, Goldsmith said.

In a related but separate project, the Port of Seattle is considering building a new eastbound exit that would allow vehicles to join southbound traffic on State Route 99.

Tim St. Clair can be contacted at tstclair@robinsonnews.com or 932-0300.