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Shared-Track: A Handbook of Examples and Applications 73 Table 25. Estimated rates of passenger fatalities for each option. Option 1 Option 2 Option 3 Option 4 Accident Scenario Full Concurrent Concurrent Concurrent Temporal Separate Shared Shared Separation Single Single Track Double (Base Case) Tracks Track Train-Train Collisions 0.0448 0.037 0.0229 0.0113 Intrusion Collisions 0.0023 0.004 0.004 0.0040 Diamond Collisions 0 0.0002 0 0.0001 All Train Collisions 0.047 0.041 0.027 0.015 Derailments 0.0075 0.0085 0.0085 0.0085 Obstructions 0.0032 0.0037 0.0037 0.0037 Grade Crossings 0.0340 0.0380 0.0380 0.0380 Total Accidents 0.092 0.091 0.077 0.066 Passenger miles 125.7 141.5 141.5 141.5 (millions) Fatality Rate per 0.73 0.64 0.55 0.46 million passenger miles application of the ATS or ATC systems, which reduce the chance of train-to-train collisions for the entire passenger operation. The other point to note is that grade crossing collisions with highway vehicles dominate the accident counts, and are unchanged by either the train control system or the presence of concurrent freight operations. The numbers of injuries and fatalities change in tandem with changes in train control system and passenger and freight operations, and can be discussed together. The principal observations are: Train collisions are responsible for about 70% of injuries and fatalities in the base case, Option 1, but this reduces to only 35% in Option 4 due to the benefits from higher capability train control systems fully offsetting the added risks from freight train operations. As casualties from collisions are reduced, those from grade crossing collisions become domi- nant, emphasizing the importance of addressing crossing hazards. The best comparison between Option 1 and other Options is the injury and fatality rates given in the last line of each table. Using rates is the appropriate way of allowing for the effect of additional ridership exposed to accident risks in Options 2, 3, and 4. These rates show a steady decrease from Option 1 levels compared to Options 2, 3, and 4. Since Options 1 and 2 repre- sent operations that are currently accepted by FRA, then it is clear that the safety performance achieved by Options 3 and 4 would be entirely acceptable. Risk parameters used in the analysis properly represent the likely real-world performance of the system. However, it will be necessary to do more to convince regulatory authorities that this is so. Most importantly, a detailed analysis of the crash performance of typical light passenger rail vehicles in collisions with freight equipment must be performed, since this is the best way to understand the practical consequences of risk. Safety Case Findings The hypothetical case study determined that the following criteria have been met for the con- current single track operation (Option 3). The process that was summarized previously offers these results: Proposed operation exceeds safety requirements typical of the transit industry; and Proposed operation has a lower estimated risk than stand alone light rail system (Option 2) in terms of rate of injuries and fatalities per passenger mile.