A bridge the latest idea to replace viaduct

Imagine an Alaskan Way Viaduct replacement 80 feet in the air, supported with columns 250 feet tall.

This so-called "signature bridge" idea is quietly being explored by the state Department of Transportation (DOT) as a replacement for the aging viaduct along the Seattle waterfront.

"It's very early concept work," said David Dye, viaduct project manager, acknowledging that this bridge would cost about the same as rebuilding the viaduct, or about $2.5 billion. That's $1 billion less than a tunnel the city wants.

When the DOT realized this summer that it may have only enough money to rebuild the viaduct, and not replace it with a tunnel, Dye asked his design team to work on some design proposals. From that came the latest idea, a six-lane "cable-stay" bridge about twice the height of the viaduct. It would be supported by four towers, each about 250 feet high.

A cable-stay bridge has taut wires that reach directly from the towers to the road deck. An example is the Highway 509 bridge over the Thea Foss Waterway in Tacoma.

It would be called a "signature bridge" because it would have architectural significance, rather than what Dye called "a utilitarian, concrete, run-of-the-mill structure."

But the plan could face strong opposition from Seattle Mayor Greg Nickels, who wants to replace the viaduct with a tunnel.

"The city is working with WSDOT [Washington State Department of Transportation] on the preferred option, which is the tunnel," said Marianne Bichsel, Nickels' spokeswoman. "The time for considering alternatives has passed."

Doug MacDonald, head of the DOT, said the bridge idea has not gotten very far at his agency. "Out-of-the-box thinking is a virtue, but at the end of the day a good plan requires more than a creative eye. This was generated from a couple of WSDOT designers working with colored ink and napkins."

MacDonald said the public is not interested in flights of fancy: "This is not a WSDOT proposal. Far from it."

Dye agreed that the bridge idea is just an idea. "This is a very early concept, slightly beyond the cartoon stage," he said.

Nonetheless, the advantages, said Dye, are that it would maintain the view of the waterfront for motorists, it could be built with the existing viaduct in place, it would be quieter on the waterfront, and it would open up the area to more light.

Among the disadvantages are that there would be no downtown exits; the huge towers would have a visual impact; and because it wouldn't have two levels, as the current viaduct does, it would be wider, which troubles MacDonald.

Dye said the four towers would be erected along the waterfront, between King Street to the south and Pike and Pine streets to the north.

Dye said the DOT has not made this bridge idea public and hasn't even briefed legislators. Rep. Ed Murray, D-Seattle, House Transportation chairman, said he knew nothing about the signature-bridge proposal. "There's a lot of conceptual ideas out there," he said. "There's an idea a minute."

Dye said he's not trying to keep the idea secret, but said it simply has not evolved beyond a concept design.

"For something like this to move forward, we would have to come to the conclusion that a reasonable time had passed and there was no money for the tunnel and we were going to move to an aerial solution," Dye said. "Then we'd look at different design concepts and this is a natural extension of the thinking."

If this cable-stay bridge becomes a serious option, Dye said, the idea would go back before the public. He doesn't know whether it would mean rewriting the environmental-impact statement.

Susan Gilmore: 206-464-2054 or sgilmore@seattletimes.com