Council OKs ideas for 520 bridge design

A future Highway 520 bridge should have narrow lanes, big lids and as few columns in the water as possible, the Seattle City Council says.

The council voted Monday in support of design principles for a new span to replace the existing four-lane bridge, which is 44 years old and could be ruined by a severe earthquake or windstorm.

Council members voted unanimously for the resolution, after working on it since last fall.

It doesn't specify support for either a four- or six-lane option. Construction is still months or years away.

State lawmakers adjourned Sunday without deciding how to fund a six-lane, $4.4 billion floating bridge across Lake Washington — but they did decide to have a mediator sort out arguments about design. They also told transportation staffers to find a place to build pontoons offsite; the Port of Grays Harbor is the leading candidate.

One bridge-design proposal, known as the "Pacific Interchange" version, would replace the Montlake Boulevard interchange with a larger, aerial junction next to Marsh Island and the Washington Park Arboretum. A tall exit bridge would cross Union Bay — near the Montlake Cut — and land next to Husky Stadium.

Montlake neighborhood residents and the North Capitol Hill Community Council support that plan. It avoids a huge interchange at Montlake, and there would be landscaped lids nearby.

The shape of Highway 520

The Seattle City Council recommends these features in a replacement bridge for the existing four-lane span.

Bridge columns: Use the "lowest feasible number" to support the elevated portions.

Minimize lanes: The council calls a possible nine-lane layout "unacceptable" through Portage Bay.

Keep park land: There should be "no net loss."

Lids: Landscaped lids over the highway should be as long as possible.

Bike lane:The bike lane should extend west to reach Montlake Boulevard at or near surface level, instead of going onto a high-level exit bridge to Husky Stadium, if a 110-foot-high exit bridge is selected.

Transit links: Exit ramps should allow bus stops close to the planned Sound Transit light-rail station at the stadium.

HOV lanes: Ban any future conversion of high-occupancy vehicle lanes into general-traffic lanes.

Source: Seattle City Council Resolution 30974

State lawmakers have endorsed a six-lane bridge with two high-occupancy vehicle lanes, but not the Pacific Interchange specifically.

The council did not endorse a particular option, but Councilmember Richard Conlin says he prefers the Pacific Interchange. "Mostly, the ball is in the court of the state," he said.

Some neighbors and activists want the city to not just take orders from the state, but to consider a cheaper, four-lane bridge as a way to reduce overall auto use and combat global warming.

"The governor and Legislature are not king and queen," said David Rudo, a Madrona-area resident.

Conlin replied: "Transit stuck in traffic is not a green alternative. Transit stuck in traffic does not reduce global warming."

The council called for a carbon-footprint analysis of pollution from different designs.

Councilmember Jean Godden emphasized that the city is not making a choice between four lanes or six.

In a preliminary engineering diagram last year, the Department of Transportation showed 15 lanes at an interchange above Lake Washington wetlands, to allow for merges, exits and high-occupancy-vehicle ramps.

Monday's council resolution calls for the state to consider deleting at least one of those ramps and it says a possible nine-lane stretch above Portage Bay is unacceptable. Lanes on the main floating span should be a foot more narrow, while the inside shoulders should be 4 feet instead of 10 feet, the council says.

Mediation talks will include the city, the state Department of Transportation, Sound Transit, communities on both sides of Lake Washington, and the University of Washington, which says it generally supports the project as long as its effects on the university are mitigated.

The mediator must file a progress report this August, then a final "project impact plan" to the governor and state legislators by Dec. 1, 2008 — an indication these debates could drag for another 1-½ years.

Mike Lindblom: 206-515-5631 or mlindblom@seattletimes.com

Information in this article, originally published April 24, 2007, was corrected April 24, 2007. A previous version of this story incorrectly mentioned that a possible Highway 520 exit bridge to Husky Stadium would cross Portage Bay. Such a bridge would cross Union Bay.