interlockingsystem

An interlocking system is a railway signaling mechanism that coordinates the movement of trains by ensuring that signals and points (switches) are set in a mutually compatible way. The system prevents conflicting routes and prevents signals from being cleared unless a safe path is established. Its primary aim is to improve safety and increase line capacity by reducing the chance of human error.

Interlockings comprise hardware and logic that enforce safety rules, including interlocking machines or processors, signal appliances, point mechanisms, and track occupancy detection such as track circuits or axle counters. The control logic ensures that a signal cannot indicate proceed if a route is not properly set or the points are not correctly aligned.

Historically, interlocking began as mechanical devices with physical locks, evolved to electrical relay-based systems, then electronic interlocking, and in recent decades to computer-based interlockings running on redundant hardware and networks. Modern systems are designed to be failsafe and to provide diagnostics, with safety certifications that vary by jurisdiction.

Operation relies on the principles of route locking and signal protection. An operator or automatic controller selects a route; the interlocking verifies all prerequisites, locks the involved equipment to prevent changes, and clears the signals for the assigned path. The system continuously monitors for occupancy and faults, and will revert to safe states if a conflict or failure is detected.

Interlocking systems are integral to railway signaling infrastructure, often interfacing with centralized traffic control or electronic signaling networks. They have contributed to safer, more reliable operation and are governed by standards addressing reliability, safety, and software integrity across different regions.