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Shared Use: Progress and Evolution 81 to use the shared tracks concurrently with a greater safety and frequency, thus improving service delivery for customers of both the freight and passenger railways. San Diego could be used as a test case for the framework proposed in Chapter 4 (the Task 9 report). The service goals and objectives would be formalized based on freight and transit service requirements. The aim is clearly to upgrade the system for full concurrent operations if required by the freight traffic densities and schedules. Different train control technologies would be eval- uated for the application, leading to installation and operation of a concurrent shared-track rail- way that fully meets the service requirements of both freight and passenger railway customers. NJ Transit River LINE New Jersey Transit's River LINE opened decades after the San Diego Light Rail system and was specifically designed with frequent concurrent shared-track operations. In contrast to San Diego, the system features conventional train control technologies to ensure fail-safe train separation and was initiated with a conventional railroad rulebook and organizational culture to facilitate shared- track operation. The system is beginning to use a novel combination of Automatic Train Stop (for passenger trains) and interlocking controlled split point derails (for freight trains) to ensure fail- safe train separation between freight and passenger trains at locations where freight trains must cross or occupy short portions of the shared-track railway during the course of the normal pas- senger service day. NJ Transit's unique combination of off-the-shelf transit and railway technolo- gies to ensure that only one class of train can occupy the shared-track at any moment in time may prove to be the key breakthrough that allows concurrent shared-track transit lines to be routinely designed, built, and operated on many urban or suburban low-density freight lines. The River LINE presents the opportunity to explore the incremental approach to improving the scope and technology of shared-track operations in a retro-fit fashion. It is a system of recent vintage designed with concurrent operations in mind but with only an incipient approach to controlling freight operations in the concurrent "fail-safe separation" mode of operation. Two years after the line opened, NJ Transit has committed to the NX signal logic (NX = entrance/exit) approach to locking out specific sections of shared-track to specific modes, recently adding approximately 2.5 miles territory to its NX zone. Other measures are being considered. The demonstration project should aim to understand the feasibility and scalability of the New Jersey approach over longer distances. NJ Transit and Conrail are interested in concurrent operations over longer lengths of the River LINE, particularly a 17-mile segment between Burlington and Trenton. Here the nature of the concurrent operation is more line-haul in nature rather than short crossing movements for which NX signal logic has been successfully applied. As a demon- stration system, NJ Transit would be encouraged to refine and document its promising approach to ensuring safety, while making efficient use of limited urban transportation assets available for the transport of passengers and freight. Barriers to Implementation This research has highlighted some of the advantages and disadvantages of the shared-track concept, even where near shared-tracks are currently practiced. None of the disadvantages is insurmountable, if shared-track is the right fit. Often, they can be overcome through technical, financial, or legal resolution. However, some more prominent barriers have subjective elements. These cases require alter- ations to the judgment of regulators or changes in the perspectives of policy makers. Since such perceptions can be based on the newness and limited experience with shared track and little expo- sure to DMU or LRV equipment, they need a stronger and more irrefutable objective argument to