Abstract: A railway signalling system includes a plurality of trackside equipments (11,12) and means (1,2,3,4,6, 15,16) for transmitting control information to the equipments and receiving status information therefrom, each of the trackside equipments being provided with a respective microprocessor (13 or 14) via which such control information is transmitted from the said means to the equipment and via which such status information is received by said means from the equipment.

Abstract: A computer based railway interlocking control system, having triple parallel redundant control computers (FIG. 2) provides greater system reliability as compared to a single computer system. The railway traffic control devices, e.g. points and signals, are arranged to be controlled by signals in one of two possible steady states, the interlocking control means (30, 31, 32, FIG. 2) is arranged to produce control signals in the steady state for de-energized or "safe" device settings and in an alternating state for energized or potentially "unsafe" settings. The alternating control signals (33, 34, 35 or 38) must be converted to the corresponding steady state to operate the devices thus, the converting or restoring circuit discriminates against dormant wrong side failures, i.e. "unsafe" signals to increase the inherent safety of the system.

Abstract: An electronic or computer-based railway control system including further safety checks in addition to normal safety interlocking. The present system carries out checks to see that operations, such as print switching and signal setting, are carried out in the correct sequence for a given route having regard to the position and movement of a train as indicated by track circuits. In a computer-based system appropriate checking routines may be written into the computer soft-ware.

Abstract: The specification discloses an electronic or computer-based railway control signal interlocking system. Signals representing the settings or conditions of railway control elements e.g. track circuits, signals and points, and their control signals are checked as usual by the interlock equipment to establish route safety. However failures in the system may only be discovered when a change to a control element setting is attempted. Since long periods can elapse between changes a failure may lie dormant for some time. In order to reduce dormant wrong side failure periods to a minimum the signals supplied to the interlocking equipment are periodically switched to a predetermined state chosen to prove that when the interlocking equipment receives the switched signal that a wrong side failure mode does not exist in the switched signal path.