Signalling block system

A signalling block system (or block system) is a safety mechanism primarily found on railways that is used to prevent trains from colliding. Block systems divide the track into fixed segments ("blocks") using signals, sensors, or other equipment, and one train may occupy a block at a time. This ensures that a train always has time to stop before getting dangerously close to another train on the same line. The block system is referred to in the UK as the method of working, in the US as the method of operation, and in Australia as safeworking.

Block systems are also commonly found on large roller coasters that can operate two or more trains simultaneously. Brakes are commonly used to stop a roller coaster train when needed.