BACKGROUND
According to the 1474.1-2004-IEEE Standard for Communications-Based Train Control (CBTC) Performance and Functional Requirements:
“A CBTC system is a continuous, automatic train control system utilizing high-resolution train location determination, independent of track circuits; continuous, high capacity, bidirectional train-to-wayside data communications; and train-borne and wayside processors capable of implementing automatic train protection (ATP) functions, as well as optional automatic train operation (ATO) functions, and automatic train supervision (ATS) functions.”
CBTC control philosophies can allow trains to operate safely at shorter headways and permit system operations to recover more rapidly in the event of service delays; all of which can offer a more regular and improved passenger service which can translate into increased line capacity constrained only by the performance of the rolling stock and the limitations of the physical track alignment. One of the fundamental operational benefits of CBTC systems is that movement authority limits are no longer constrained by physical fixed-block boundaries but are established through train position reports that can provide for “virtual block” or “moving block” control philosophies.
According to FTA Report 45, An Assessment of the Business Case for Communications-Based Train Control:
“To date, deployment of CBTC technology within the United States has been limited, due, at least in part, to a perception of higher costs associated with the implementation of this technology. This perception of higher costs is in turn driven, in part, by a perception that CBTC systems require a secondary track circuit-based or axle counter-based “fall-back” system to detect and protect trains in the event of CBTC system failures.”
Research is needed to provide guidance to transit agencies considering CBTC, particularly as it relates to secondary train detection/protection systems.
OBJECTIVE
The objective of this research is to develop guidelines to enable a transit agency to evaluate the need for (1) secondary train detection/protection systems or (2) operating practices in lieu of detection/protection systems when implementing a CBTC system.
Accomplishment of the project objective will require at least the following tasks.
TASKS
Phase I
(1). Based on a review of literature and interviews with suppliers, owners, and operators, critically review North American and international in-service, in-progress, and planned CBTC systems and the extent to which any secondary systems have been used. The review should include:
- considerations for design, safety, operations, fleet interoperability, commissioning, lifecycle cost breakdowns, and residual risk; and
- options for assuring safe operations through secondary systems and practices.
(2). Develop a detailed work plan for Phase II. Identify proposed Phase II case study sites and develop a plan for conducting the case studies. Prepare a detailed outline for the Task 5 guide.
(3). Prepare an interim report that includes the results of Task 1 and Task 2.
Phase II
(4). Conduct the approved Phase II work plan to develop case studies that demonstrate implementations of CBTC, with and without secondary systems, illustrative of tradeoffs made in procurement/operations decisions. (5). Prepare a transit agency guide to evaluating secondary train detection/protection systems in communications-based train control (CBTC) systems. Include illustrative uses of the guide for hypothetical decisions regarding CBTC secondary systems. The guide shall include definitions of terms, illustrative case studies, and hazard analyses drawn from domestic and international practices. The guide shall also define alternate processes that might be used in lieu of a secondary system. (6). Prepare a stand-alone technical memorandum titled “Implementation of Research Findings and Products.” (7). In addition to (a) a transit agency guide to evaluating secondary train detection/protection systems in communications-based train control (CBTC) systems, the final deliverables for the project should include (b) a final report summarizing the work, (c) an updated interim meeting PowerPoint presentation suitable, upon revision, for posting on the project website, and (d) the Task 6 implementation technical memorandum.
STATUS: Complete. Published as TCRP Web-Only Document 71: A Transit Agency Guide to Evaluating Secondary Train Detection/Protection Systems in Communications-Based Train Control Systems. The WOD provides a practical approach to evaluating the appropriate level of secondary train detection/protection systems (STD/PS) for a given communications-based train control system application. In terms of detection, track circuits and axle counters are both considered and compared, including the broken rail detection capabilities of track circuits and the possibility of having no secondary detection at all.
The first part of this guide presents different technologies, and discusses communications-based train control deployment trends and feedback on operations from rail transit agencies around the world. The second part provides guidance for selection of an appropriate level of STD/PS, in terms of candidate technologies, product maturity, and potential risks. The document is accompanied by a PowerPoint presentation.
