Coordination between trains in the tunnel is managed by the Link Light Rail Operations Control Center (OCC), located at the King County Metro Communication and Control Center in SoDo. The OCC controls vehicle movements (and formerly operations between buses and trains) by using on-board radio-frequency identification tags installed on tunnel buses and light rail vehicles, their locations tracked by passing over induction loops embedded in the tunnel roadway. Signals at each station indicate when a driver can proceed through the tunnel. Within the DSTT, bus speed limits are set at in stations and staging areas and between stations. During joint operations, Light rail trains and buses were required to wait in the tunnels between stations until the platform was cleared of vehicles ahead; buses were mandated to keep a minimum of six seconds of separation between each other.