Midweek Video: WSDOT’s New SR-520/I-5 Connection for Transit

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The Washington State Department of Transportation has awarded a $68 million contract to Walsh Construction to build a new ramp connection between SR-520 and the I-5 reversible express lanes. This will allow transit — and eventually carpools — to have direct access to the I-5 reversible express lanes. Currently, vehicles only have access the I-5 mainline lanes to and from SR-520. This new connection could help bus routes (e.g., Routes 257, 311, 424, and 545) save time on a critically congestion section of I-5 between SR-520 and Downtown Seattle.

The new connection also provide access to an improved on- and off-ramp at Mercer Street. This reduces the need for weaving to and from the SR-520 lane connection on the I-5 reversible express lanes and could open up new possibilities for cross-lake bus routes to South Lake Union and Uptown, though increasingly transit agencies are emphasizing the light rail connection at University of Washington Station. SR-520 bus routes would also have access to other southern on- and off-ramps in Downtown Seattle via the I-5 reversible express lanes, so this seems likely the biggest benefit of the project to transit.

Initially, this new connection would only be for transit, but once the Portage Bay Bridge and Roanoke Lid Project is completed (estimated to be 2029) on SR-520, the lanes will open to all carpools, which presumably means vehicles with three or more passengers if SR-520 regulations apply. However, this new connection is not without its problems as it will encourage more motorists to drive — albeit at a little higher occupancy level — on SR-520 and I-5. This by extension further reinforces suburban sprawl, vehicles miles traveled, and car ownership. So it begs the question if carpool access is a prudent choice. Wouldn’t it be better to restrict access on the new connection between SR-520 and I-5 reversible lanes to only transit so as to principally encourage transit use and better ensure bus speed and reliability?

Construction on the project is expected to be completed in late 2023.

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Stephen is an urban planner with a passion for sustainable, livable, and diverse cities. He is especially interested in how policies, regulations, and programs can promote positive outcomes for communities. Stephen lives in Kenmore and primarily covers land use and transportation issues for The Urbanist.

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AJ M

I think you framed it correctly at the end. As long as no material impact to the speed/reliability of buses, I don’t see a reason to exclude carpools. I’m skeptical that improved HOV infrastructure induces VMT; any induced carpool trips should be more than offset by the mode shift from SOV to HOV.