Practicable Safety: Train Protection System Evaluation

Standards relating to the development of safetyrelated systems containing software tend to focus on the requirements that need to be met in order to ensure that a system of the expected integrity is delivered. These standards are establishing benchmarks which customers and regulators are now specifying. The problem is that if a high integrity system is required, it may be uneconomic because of the demands specified in the standards. However a lower integrity system may provide a significant safety benefit and be economically viable. To accept a lower integrity system, contrary to the standards or even “best practice”, there needs to be a robust cost/benefit case. This paper shows by example the use of cost/benefit analysis in relation to a public transport safety issue.