of its trips into the tunnel. 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, 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. During joint bus–rail operations, two types of vehicles were used in the Downtown Seattle Transit Tunnel: Sound Transit's Kinkisharyo-Mitsui light rail vehicles and King County Metro's New Flyer diesel-electric hybrid buses. The New Flyer buses, dubbed "tunnel buses" by King County Metro, were ordered in 2004 to replace a fleet of Breda dual-mode electric trolleybuses whose overhead wire was to be removed in the tunnel's renovation for light rail; 59 of the dual-mode Breda coaches were converted into fully electric trolleybuses between 2004 and 2007 and moved to surface routes, where they continued to operate for more than a decade before being fully replaced in 2016. The New Flyer low-floor, articulated buses feature a "hush mode" that allowed buses to operate solely on stored electric power within the tunnel, minimizing emissions and noise. History Previous subway proposals Several proposals for a cut-and-cover subway tunnel under 3rd Avenue in Downtown Seattle were presented to the City of Seattle by predecessors of the Seattle Planning Commission throughout the 20th century. The first major proposal was part of urban planner Virgil Bogue's "Plan for Seattle" in 1911, as Route 1 of a proposed rapid transit network. Route 1 ran southeast on 3rd Avenue from a circular ring around a proposed civic center in the Denny Regrade neighborhood to King Street Station, paralleled to the west by a subway on 1st Avenue known as Route 17; stations on the line were to have additional entrances from department stores and other major businesses on 3rd Avenue. The plan was supported by City