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Shared-Track: A Handbook of Examples and Applications 75 frequently. Some time after the opening of the Orange Line, the FRA disallowed the freight operations while light rail vehicles were on-line, resulting in effective temporal separation. The commingled operations on the fringes of the service day were outlawed. 2001: Restricted parallel single track operation. FRA later relented somewhat and allowed movements on separate tracks under highly restricted conditions. In 2001, the FRA granted a waiver to SDTI to permit its continued operations under a petition for "grandfathering" the previous practices. However, several aspects were restricted. This operating scenario was termed "limited night-time joint operation." It was not permitted for westbound movements on the Blue Line due to a potential single-track conflict. 2004: Scripted Temporal Separation. In 2004, a further waiver was granted to allow limited night-time joint operations for westbound movements on the Blue Line. Under the federally approved Standard Operating Procedure (SOP), one freight train is allowed to operate on one track while one trolley is allowed to operate on the other during the fringe period. The west- bound freight train must come to a complete stop at a predefined meeting place on the double- track mainline before the SDTI dispatcher can release an eastbound trolley from the yard with signal indication. The trolley must pass the standing freight train at no more than 20 mph. SOP reflects considerable caution regarding the possibility of overlapping authorities being granted by the train dispatcher, the possibility of trains exceeding movement authorities, and the possibility that freight train lading will intrude into the path of the passenger train. Under SOP, the two tracks are treated like two, almost independent, single track railways. During this carefully scripted mode of operation, the light and conventional rail vehicles remain spa- tially and temporally separated. NJ Transit Newark City Subway 2001: Temporal separation. One Diamond Crossing with a freight carrier; 19 hour passenger window; 5 hour freight window five nights per week; impacts late night passenger movements. 2004: Short interval temporal separation (one mode at a time separation). Added vital signal protection with automatic train stop and interlocking at diamond, and central control of movement. NJ Transit River LINE 1999: Temporal separation. Two Diamond Crossings with 24 hour access, then approximately 30 miles of mainline track; 16 hours passenger window; 8 hour freight window; transit vehicle equipped with automatic train stops (ATS), freight movement controlled by derail. 2007: Extended temporal separation. Added another 2.5 miles of shared track by using entrance/ exit control over three interlockings. Applied ATS and derails to permit use by one mode at a time. Achievable Incremental Steps The incremental approach now has a credible foundation. Furthermore as regulators and pol- icy makers gain more experience with sharing track, these examples can be replicated in other settings. The increments can be separate or combined: Scripted temporal separation: carefully defined procedures and scheduled movements; Short interval temporal separation: the period of temporal separation is not precisely defined by law, but it is implied. This technique positively restricts the train movements (i.e., separates them) for limited but shorter periods. These shorter operating windows are shifted from freight to passenger to freight more frequently within 24 hours, rather than only once; Extended temporal separation: applies vital train control technology to increasing portions of the route, thus enforcing fail-safe train separation over more track.