The State Route 99 tunnel under Seattle reopened early Saturday morning after it was shut overnight for maintenance.
During the closure, crews updated fire control system software This temporarily deactivated the system, which is why the tunnel closed overnight.
Crews also inspected jet fans, cameras and overhead signs. They also swept the road of debris.
Monthly maintenance typically requires the closure of just one direction of the tunnel. In July, crews will resume the regular schedule and close the northbound lanes.