State offers 3 decidedly different designs for viaduct

Imagine a new Alaskan Way Viaduct with a park on top and garage doors that can roll down to block out some of the noise.

Or maybe a new viaduct built on towers 14 stories tall with the roadway twice the height of the existing viaduct.

While the state has decided how it would build a tunnel to replace the viaduct, the shape of a possible new elevated structure is very much is flux.

So much so that the state Department of Transportation (DOT) on Tuesday presented three new ideas to the Seattle City Council, which is on record supporting the tunnel.

"We need to have the project ready in a couple of years so we need to cover our bases with the elevated structure," said Ron Paananen, viaduct project director with DOT. "We don't want to get a year into it and be asked if we considered other options."

He said the state initially considered nine alternatives for rebuilding the viaduct, but five were impractical and the state narrowed the list to four. One is the plan that has been evaluated in the environmental-impact statement: another stacked roadway about 50 percent wider than the existing viaduct. That is estimated to cost from $2 billion to $2.4 billion.

Paananen said no cost estimates have been made for the new options, and the state is hoping they will be available next month.

Two of the new designs would be side-by-side roadways; the third would also be two roads abreast, possibly with parts on different levels. They all would be much bigger than the existing viaduct.

"This clearly shows that all the options for a new aerial structure are massive," said Marianne Bichsel, spokeswoman for Mayor Greg Nickels, who is pushing for a tunnel. "The message here is any aerial structure is much, much larger, while a cut-and-cover tunnel adds about 30 acres of public space to the waterfront."

Paananen said the driving force for the new aerial options is an attempt to keep the viaduct open during construction. The three new designs would allow that, he said.

• A new viaduct built similar to the West Seattle Bridge, where the northbound and southbound roadways each would be mounted on large support columns, with 300 feet between each column. This would be a side-by-side viaduct, although the roads could be at different elevations in places.

This viaduct plan would call for a structure 105 feet wide, and it could be 100 feet high. The overall effect would be twice as wide as today's viaduct, but with fewer columns.

• A cable-stay bridge, which has taut wires that reach directly from the towers to the road deck. The towers would be 140 feet tall, the equivalent of 14 stories. It would be a single-level bridge, with side-by-side roadways, and 110 feet wide — about twice the width of the current viaduct. The road would be 100 feet above Alaskan Way. There would be 450 feet between columns, which means there would be only six columns along the central waterfront.

This would be the tallest and widest of all the elevated options under consideration.

• A side-by-side roadway with a park on top. It would be built west of the existing viaduct, almost to the edge of Elliott Bay. Alaskan Way would be built underneath. On top would be a park, 10 acres of green space, said Paananen. Under this proposal, huge garage doors, designed with art, could be pulled down on the sides of the roadway during the height of the commute to block some of the noise.

Listening to the new proposal, members of the council seemed skeptical, asking questions but saying little about the ideas.

Councilman Richard Conlin had one comment: "I commend your creativity."

Paananen said the state needs to make a decision on an elevated structure by the end of the year to prepare for a final environmental-impact statement.

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