Safety critical software in traffic control systems

Because of the safety implications, certain conditions in road traffic signal systems must be avoided, and it is not acceptable for them to be discovered once the system is in use. The article identifies relevant factors. First, all potential hazards must be identified. The specification needs rigorous analysis; the specifier may be unaware of the types of problems arising in software. Formal methods of testing and analysis are considered. The use of tools in software development, and particularly for detecting unforeseen consequences of apparently slight changes in software, is discussed