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32 Shared Use of Railroad Infrastructure with Noncompliant Public Transit Rail Vehicles: A Practitioner's Guide Proving the system also may include other activities such as: Test plans, procedures, and reports--normally defined in procurement documents; Maintenance--inspections and periodic testing--addressed in 49 CFR Part 234 and 236 tests; and Verification and validation--typically required for software based systems. 7) Practical Considerations for Shared-Track Because of its impact on safety, train performance, and operator behavior, the selection of a train control system may be the most significant choice for a transit agency considering shared- track. Transit-like (25 minutes) headway is not envisioned on shared-track lines. Most likely, an occasional freight move is required along the corridor during an off-peak period when the transit vehicles are running at 2030 minute intervals. In some cases, the last few passenger trains of the day would overlap with a freight train switching on-line industries. Train control can be the dominant influence on the regulatory review process and directly affect the viability of the project. The choice of technology is influenced by many considerations. Some of the most important are: Current train control technology is mature and offers little room for improvement. Marginal improvements are achieved at significant cost. Absent a strong business case, there is little incentive to change or upgrade the technology. Design, manufacture, and installation of train control systems are expensive and require a long lead time. Once in place, train control systems are not readily adaptable to changes in tech- nology or operating patterns without incurring substantial costs and time-consuming field modifications. Railroads and regulators can be very conservative in adopting new technologies, particularly where safety is affected. The FRA staff carefully scrutinizes any divergence from requirements of 49 CFR Parts 234 or 236. While deviation from regulations is sometimes incorporated, each must be justified to the FRA case by case. The system must be suitable for both freight and passenger equipment. It also must fulfill owner specified requirements and support the service plan envisioned. 8) Issues Unique to Train Control for Shared-Track When choosing a train control system, the prospective operator is advised to develop a design that meets FRA regulations and acknowledges the need to submit a waiver petition to the FRA. The system designers and operators should engage the Federal authorities as early as possible to engineer an acceptable train control system. Any request for relief from Federal requirements must be justified. The following technical choices may encourage a favorable regulatory review and acceptance by the freight operator. 1. A train control system that provides fail-safe train separation is essential for concurrent operations. 2. The train control system should favor the transit operation and accommodate only an occa- sional freight movement among off-peak passenger service. 3. The design should consider the needs of the freight operator in addition to standard passen- ger rail service requirements. To enlist cooperation of the freight operator, the benefit of a new train control system should be quantified. 4. Designers should consider vehicle shunting characteristics for both conventional and light rolling stock, for track circuits, and grade crossing warning systems.