King County Metro Transit (King County Metro) has begun construction on the RapidRide I Line, which will span 17 miles in Renton, Kent and Auburn, Wash., starting in 2027. The RapidRide I Line will improve rider connections in the regional system, including the RapidRide F Line, Sound Transit buses and the Sounder commuter rail Kent and Auburn stations. 

The RapidRide I Line will use hybrid electric buses on the route, with weekday service every 10 to 15 minutes during the day. Weekend service will offer 15-minute frequencies throughout the day. As Mass Transit magazine previously reported, the route will feature nearly two miles of bus-only lanes and transit signal priority to support faster, more frequent service. Riders will also experience off-board fare payment and all-door boarding.  

Features of the RapidRide I Line include: 

• 82 stations along the route with new features designed to improve customer safety and comfort. 

• Improvements at 27 intersections and 12 business access and transit lane widenings to enhance bus speed and reliability. 

• 64 new or enhanced pedestrian crossings and over 100 new ADA accessible curb ramps to improve pedestrian safety and access. 

In January 2025, King County Metro received a $80 million grant from the Federal Transit Administration's Capital Investment Grants program to support the project. More information on the project can be found on the project's website.