Northbound HOV3Transit I-5 express lanes entrance at Mercer Street in Seattle opens May 12

The Washington State Department of Transportation will open a new northbound HOV3+ and transit entrance to I-5 express lanes at Mercer Street on May 12. This new entrance allows HOV3+ vehicles to access the express lanes from the left side of Mercer, utilizing a ramp that was previously exclusive to southbound traffic. This change is part of the larger SR 520/I-5 Express Lanes Connection Project, which aims to enhance traffic flow for HOV3+ vehicles. Crews added a concrete median barrier in 2024, enabling the express lanes off-ramp to serve as a reversible ramp. Non-HOV3+ travelers will continue to use the existing entrance, maintaining traffic flow for all vehicles.

Alongside this, ramp metering will adjust based on the direction of express lanes, impacting how northbound travelers enter I-5. The new entrance will initially serve only northbound traffic, while a flyover ramp connecting to SR 520 is expected to open in 2031. This development is crucial for improving transit options in the Seattle area, particularly for high-occupancy vehicles.