200602 – Traynor – Safe Platforms for the Integrated Control of Railways

Railway operators are becoming increasingly “corporately” aware of the need to take a more holistic view of safety, particularly the adverse commercial and legal consequences that are attendant upon poor safety performance. There is a growing trend to viewing the railway as a complete system where we no longer consider “Islands of Safety”, but rather view safety as a systemic characteristic of the whole railway.

At the operational level, there is a growing recognition that systems used for “Train Control”, as well as ancillary functions such as tunnel ventilation, traction power, CCTV etc. whilst not safety-critical, nevertheless play a role in overall railway safety and are therefore “safety-related”. Specifically, control systems are now often required to perform some safety functions, to Safety Integrity Level 2 (SIL 2). These systems must go through a rigorous safety approvals process before being accepted into service. For example, Network Rail (UK) plc publishes a “Yellow Book” (refer Engineering Safety Management [5]), which imposes onerous safety management obligations on suppliers of safety-related systems. Our Hong Kong customers impose similar requirements (refer KCRC publication System Safety Management Requirements for ERE Contracts [1]).