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Enabling Shared-Track: Technology, Command, and Control 33 5. System designers should incorporate a complementary approach to the human interface of the train control system, including: (a) a full function control-center; and (b) appropriate operating Rules and Procedures. 6. The system must accommodate a transition between line-of-sight street running (if the sys- tem has a street running portion) and cab signaled territory. Light passenger rail cars must not enter shared territory without functioning cab signals without a safe operating protocol; con- ventional equipment must be prevented from entering street running sections by accident. The objective is to use signal technology to prevent collision hazards by enforcing movement authority. No new technology is necessary, but the train control system must provide the mini- mum required feature set defined here, including the fail-safe train separation requirement and an emphasis on local hazard mitigation technology using auxiliary safety critical systems. All com- ponents are readily available in off-the-shelf configurations from multiple full service and spe- cialty vendors. However, application of current technology to novel situations may be required. Auxiliary Safety Critical Systems Safety concerns for track sharing are compounded due to structural disparity between con- ventional equipment and light passenger rail cars. Four issues are especially prominent shared- track concerns. 1. Intrusion Detection. Advance warning of encroachments on the light rail train clearance envelope. Two types exist, continuous and point detection. One such device is illustrated in Figure 3: 2. Hazard Detection. Prevention or warning of failures in freight equipment or other hazardous conditions that could result in derailment, such as rock slides, hot axle boxes, or dragging equipment. Detection devices may be necessary where freight is operating nearby, preferably close to limits of shared-track zones. 3. Roll-out Prevention. Prevention of freight equipment roll-outs from sidings or at crossings, onto the main line used by a light rail train. Typically derails and electric locks are used for this protection. 4. Broken Rail Detection. Detection of rail failures, potentially averting derailments. This func- tion is typically provided by a track circuit. Placement of these systems should consider volume and speed of the freight traffic, train length, type of cargo, terrain, gradient, track centers and visibility. If feasible, fixed barriers and Laser Field (approx. 3 inch wide) Laser Scanner Alarm Point Figure 3. Intrusion detection technology.