Arboretum Bypass Plan for 520 bridge lauded by experts

For the past few months, the Washington State Department of Transportation (WSDOT) has been mulling over possibilities for replacing and expanding the Highway 520 bridge across Lake Washington.


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Craig Dalby, a concerned resident of Seattle who endures the daily commute across the bridge, came up with a possible solution that could save the Arboretum and significantly reduce the amount of traffic along Montlake.

"The Arboretum Bypass Plan restores the Arboretum to its pre-1960 appearance," Dalby wrote in his proposal. "No Arboretum plant specimens are damaged, and the existing freeway is removed from the landscape."

Dalby, a Geographic Information Systems Specialist for the National Park Service, is inexperienced in the field of engineering, but has received nothing but praise for his new design.

"The UW Botanical Gardens Committee (UWBGC) looked at it and we were very impressed," said Elizabeth Loudon, Education and Outreach manager for the UW Botanic Gardens. "It's really the best option that we've seen so far in terms of effects on the Arboretum."

The Arboretum Bypass Plan, as Dalby's design is called, proposes a four-to-six-lane bridge that would be constructed north of the existing 520 bridge, heading to the opening of Union Bay midway between Madison Park and Laurelhurst.

It would then curve north until it comes to shore just northeast of Husky Stadium.

From there, Dalby suggests a tunnel be constructed under the Montlake Cut, bringing cars back up to the street along the current freeway near Portage Bay.

Ramps would then connect from Montlake Boulevard to the freeway to the west.

The plan completely removes the bridge from the Arboretum lands, and allows room for the possibility of a light rail in the future, an element that other alternatives to 520 have not included.

"It's ridiculous to build a bridge that won't provide for mass-transit in the future," Loudon said. "And especially with global warming, we should be looking ahead."

While it is still in the conceptual phase right now, Dalby's plan has been widely accepted, garnering positive reactions from the UWGBC as well as the United States Department of the Interior.

According to a letter from the Department of the Interior to WSDOT, "At least conceptually, this specific example presents itself as a possibly prudent and feasible alternative."

Another top contender for the replacing of the 520 bridge is the Pacific Interchange Plan.

This plan also calls for moving the bridge northward, but will still run through the Arboretum as it does now, with the addition of a high-level overpass beginning on Foster Island, crossing over Marsh Island and ending just northeast of Husky Stadium, Dalby said.

While this plan has been among the top of WSDOT's proposals, Loudon and the UWGBC agree it appears to have a more negative impact than Dalby's, on both the environment as well as traffic.

"It would not only significantly widen the streets, it would funnel the traffic onto [Montlake and Pacific]," she said, "and it's already overloaded with cars as it is."

Dalby feels his plan would significantly reduce traffic flow, pollution and noise through the Montlake neighborhood, as the freeway ramps would be moved north of the Montlake Bridge and would protect the salmon migration route convergence zone in the waters below.

While the Arboretum Bypass Plan still needs to be tested for feasibility and practicality, Dalby has spoken to residents in the Montlake neighborhood as well as the UWGBC and even the governor's staff about the issue.

Reactions have been enthusiastic about an environmentally sound alternative to the existing bridge.

"It's the best alternative seen so far," Loudon said.

Reach reporter Brittany Rogers at news@thedaily.washington.edu.

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