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74 Shared Use of Railroad Infrastructure with Noncompliant Public Transit Rail Vehicles: A Practitioner's Guide Results of the Sample Case Study In this example, congruent results of the business and safety cases are integral to concluding that a shared-track project is feasible for the defined circumstances. Positive indications are: In terms of capital cost, proposed shared track operation is more economical than a separate and parallel (stand-alone) light rail system sharing a corridor with the freight branch. Although the temporally separated operation (Option 1) requires lower capital investment than the proposed operation, it does not fulfill the service needs of either the freight railroad or the transit customers, and suppresses the expansion of business for both track users. The Business and Safety Cases--What Works in the Real World The approach that has succeeded is evidenced in projects that commenced service in accor- dance with the temporal separation policy. The evolution of rigid temporal separation to near shared-track is reflected in real-world examples. Each of the systems cited below was begun to serve a particular transit need. Each started out simple and added complexity in response to a need. This need was apparent to both the transit and freight operator and resulted in improved capacity and flexibility for both modes. Services modifications are achievable. System safety fea- tures are based on traditional railroad technology and verifiable and use practices easily under- stood by the FRA. Operating rules and procedures adopted by the transit system closely resem- ble those of the freight railroads. In both cases the transit agency calculated a reasonable cost benefit ratio that justified the improvement. The incremental changes to these systems were mer- ited by the business case and were deemed acceptable by the safety case. Some were in service long before the 1999 Joint FRA/FTA Policy. Others began after 1999. Progress made by current operating systems offers both guidance and confidence to prospective operators. The experience of operating these hybrid systems, in conformity with a policy that previ- ously was non-existent, required educating both operators and regulators. Regulators were and are knowledgeable about standard railroad technology, but at the inception of shared use, unfamiliar with noncompliant transit vehicles, their performance capabilities, and light rail operations. Additionally in 1999, the FRA introduced new and significantly revised regulation putting great emphasis on structural integrity and passenger safety, which influenced their per- ception of shared-track. San Diego Trolley 19811989: Commingled operation. San Diego Trolley's track-sharing practice is both the ear- liest and the most advanced example of a shared-track rail corridor operating in North Amer- ica. On both the Orange and Blue Lines in San Diego, freight trains operate almost every weeknight under FRA waivers. The San Diego Trolley, Inc. (SDTI) track sharing operation commenced in 1981, when trolley operations began on the Blue Line to the international border on half-hourly headways. Initially, the operation was fully commingled, with freight trains operating in the slots between light rail trains. This historic practice was extended to the Orange Line when trolley service began on that line in 1989. Neither of these commingled operations resulted in mishaps or injuries. The shared-track segment consists of 13.5 miles on the Blue Line, and 17.0 miles on the Orange Line. 1990s: Commingling terminated reversion to temporal separation. As transit service demand in the corridor increased during the mid-1990s, and headways were reduced from 30-minutes to 15-minutes, freight operations were moved to the early morning hours. Commingled oper- ations continued on the fringes of the transit service day, when light rail trains ran less