Image courtesy of WSDOT
The Washington State Department of Transportation plans to construct an HOV-only connection from State Route 520 to the Interstate5 express lane to Mercer Street starting in 2020.
Image courtesy of WSDOT The Washington State Department of Transportation plans to construct an HOV-only connection from State Route 520 to the Interstate5 express lane to Mercer Street starting in 2020.
WSDOT plans to begin constructing a reversible HOV-only connection from State Route 520 to Mercer Street via Interstate 5 express lanes next year, providing an easier commute between South Lake Union and the Eastside.

The project will be built in conjunction with the Montlake Phase of the SR 520 Bridge Replacement and HOV Program, which includes a new West Approach Bridge South for eastbound traffic that will connect to the floating bridge over Lake Washington, a lid over 520 and a bicycle/pedestrian land bridge east of the lid that connects the Washington Park Arboretum and East Montlake Park, and a major revision to Montlake Boulevard to accommodate the new bridge. The entire process is slated for completion in 2023.

“Originally, we had coupled this with the next phase of construction, called the Portage Bay phase, but we found a way to decouple this and get this reversible HOV connector built quicker,” said WSDOT spokesperson Steve Peer. “The connector is so close to where the new lid is going to be, it’s all in that same area, so it’s easier to do it piecemeal.”

WSDOT plans to make the new connector ramp and HOV lane open to buses first, and then carpools once SR 520 is complete. The I-5 reversible express lanes will be restriped to retain the existing four lanes.

Traffic will be accommodated westbound from SR 520 to the southbound I-5 express lanes during morning peak hours, and then northbound on I-5 to eastbound 520 during evening peak hours.

“The Mercer Street ramp would have a reversible lane control system with swing gates. It would be illuminated with overhead lights and have signage alerting drivers about the status of the ramp,” according to WSDOT documents.

WSDOT has requested a three-year nighttime construction noise variance from the Seattle Department of Construction and Inspections, arguing it will save money and avoid exacerbating existing congestion on 520, I-5 and the Mercer Street corridor.

Peer said there will likely be times during the project when traffic impacts will occur.

WSDOT’s application states only working during the day would “require multiple significant closures of SR 520 and I-5,” not only hampering traffic, but also adding between $2.6 million to $9.4 million to project costs. The economic impact of traffic delays is estimated at between $90 million and $280 million.