Interlocking systems

thumb|The tower and tracks at Deval interlocking, Des Plaines, Illinois, in 1993 In railway signalling, an interlocking is an arrangement of signal apparatus that prevents conflicting movements through an arrangement of tracks such as junctions or crossings. In North America, a set of signalling appliances and tracks interlocked together are sometimes collectively referred to as an interlocking plant or just as an interlocking. An interlocking system is designed so that it is impossible to display a signal to proceed unless the route to be used is proven safe.

design of a signalling box for controlling railway operations without mechanical switches or relais