Safety Certification of a Modern Train Control System Implemented on an Existing Line - Lessons Learned From The NYCT Canarsie CBTC Project

About a decade ago New York City Transit embarked in a large program to modernize their aging conventional signal system. A Communications Based Train Control system (CBTC) was selected to equip the Canarsie line as a pilot project. The technology was chosen based on the CBTC system capability to: - Enhance safety - Increase performance (throughput, availability) - Implement specific users / functional requirements - Reduce long-term life-cycle cost of the signal system NYCT is not under Federal or other mandated regulations pertaining to the safety certification of systems or equipment, and is thus self-certifying the safety of the CBTC System for the Canarsie Line. This, combined with the fact that such modern train control system was the first one implemented on its network, NYCT was facing a unique challenge in defining the right safety certification approach to be followed. Instead of providing a chronological description of the safety certification process as it was implemented, this paper provides a description of the most important challenges and issues NYCT had to address. It explains the approach taken for each of these challenges as well as the lessons learned. The following challenges are discussed throughout this paper: - Self certifying environment - Handling safety-related modifications from the baseline product - Testing and safety approach - NYCT hazards management - Risk assessment - Safety certification updates