The Walsh Group is extending SR 520’s new transit/HOV system to I-5 via by constructing a dedicated, reversible connection between SR 520 and the I-5/Mercer Street interchange via the I-5 express lanes. (WSDOT photo)

Crews from the Walsh Group began constructing a new flyover ramp that will connect State Route 520 directly to the I-5 express lanes.

The contractor set the foundation for that ramp — steel girders — over the weekend of May 19 to 21.

The contractor set and assembled 15 large steel girders that were 75-to-100-ft. long, 5-ft., 5-in. tall and weigh approximately 36,000 lbs.

In all, it involved two crews of 25 construction workers from Walsh working alongside WSDOT inspectors and traffic operations over four shifts to execute the job. The result was a new bridge in one weekend and northbound I-5 was closed for only 15 hours late Friday night into Saturday afternoon.

This project —valued at $68 million — is extending SR 520's new transit/HOV system to I-5 by providing a dedicated, reversible connection between SR 520 and the I-5/Mercer Street interchange via the I-5 express lanes. The new reversible lane will work in concert with the I-5 express lanes. When the I-5 express lanes are operating in the northbound direction, the new ramp will connect to eastbound SR 520. The new ramp will connect westbound SR 520 vehicles to the I-5 express lanes when they are operating in the southbound direction.

Walsh Group also will be responsible for the construction of 23 retaining walls; five ramps (full depth replacement of the roadway cross section, utilities and walls); a new, three-span steel girder bridge; and reconfiguring an existing southbound off-ramp.

Overall, the project encompasses:

• Building a new, reversible transit/HOV ramp between SR 520 and the I-5 express lanes;
• Restriping I-5 express lanes to retain the four existing lanes while adding a reversible transit/HOV lane between the I-5/SR 520 interchange and Mercer Street;
• Modifying an existing ramp for reversible operations between the I-5 express lanes and Mercer Street.

Construction of this project is the second of four SR 520 projects that make up the Rest of the West improvements. The projects were funded in 2015 in the Connecting Washington funding package.

This project is on track for a spring 2024 completion.

The milestone marks a new look for Interstate 5 in downtown Seattle for the first time in nearly 50 years.

Initially, only buses will use the connection. Later, when construction of the SR 520 — Portage Bay Bridge and Roanoke Lid Project is complete and a new lane is available to receive the connection, the reversible lane will also be open to carpools.

"When complete, this project will provide a reliable transit link between the region's major employment centers in Seattle's South Lake Union and the Eastside via SR 520," said Program Administrator Omar Jepperson.

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