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6 Shared Use of Railroad Infrastructure with Noncompliant Public Transit Rail Vehicles: A Practitioner's Guide technology may reduce operating costs, or provide life cycle savings, but well thought-out and appropriate applications of common train control technologies can furnish acceptable safety and fail-safe train separation. Conventional intermittent or audio frequency cab sig- nals are sufficient for a new installation. Technologies for Achieving Fail-Safe Train Separation The single most important requirement in a shared-track system is to provide active safety. An active safety system is fail-safe, in that an inevitable human operator failure should not result in catastrophic consequences. Two currently available classes of train control tech- nologies can meet that requirement. 1. Inductive warning system with stop enforcement. Inductive warning systems provide intermittent wayside-to-train communication via a series of electro-magnets or transpon- ders installed at periodic intervals in the right-of-way. The train speed or warning can be acknowledged, but the system must slow down or stop the train regardless of whether the warning was acknowledged. 2. Coded-track circuit cab signal with speed enforcement. Coded track circuit systems provide continuous wayside-to-train communication via a pulse code or an audio fre- quency signal. The on-board microcomputer restricts train speeds and issues brake commands automatically based on the maximum permissible speeds or stop, indicated by the code. Operating rules govern the movement of equipment with failed train control apparatus. Typically, movement is not permitted without on-site supervision. Movement of conven- tional trains with failed train control apparatus would not be permitted except under tem- poral separation. Intrusion accidents and derailment risks are a threat to safety. Intrusion risks are greater in areas of close clearance. Derailments could lead to intrusion accidents. To provide safe- guards against these accident scenarios, designs featuring wider track centers and downward sloping industrial sidings should be adopted where possible. Active detection also may be necessary: 1. Proven railroad technologies: hot bearings, high-and-wide equipment, and brittle wire detectors; 2. Hazard detection technologies: optical or newer laser technologies for intrusion detec- tion and other temperature sensing devices for hot bearings; 3. Interlocked derails: prevents runaway loose cars from fouling mainlines; and 4. Electric locks and switch position indicators: minimizes facing-point derailments. Together, these technologies provide a safe operating environment. Application of these tech- nologies to mitigate identified hazards would be viewed with favor by regulatory authorities. Grade Crossing Hazards Grade crossing collisions with highway vehicles are a serious problem for all passenger and freight rail operations and some light rail systems. Crossing accident risks are not changed by either concurrent or temporally separated shared-track. Waiver applicants should emphasize the crossing safety benefits of lower vehicle mass, shorter trains, lower speeds and more powerful brake systems of light passenger rail cars compared with con- ventional commuter trains. There can be no objective technical justification for applying a higher grade crossing safety standard to shared-track than to light rail operations.