route

In railway signalling, a route is a predetermined path through a network of track sections and junctions that has been set up and locked by the signalling system to allow safe passage for a single train. The route extends from an entry signal (the starting point) through one or more block sections to an exit signal at the destination. Once a route is set and locked, all points (switches) along that path are held in the correct position, and conflicting routes that would allow another train into the same sections are prevented from being set.

Routes are created through a control interface, either manual levers in older installations or pushbuttons and track diagrams in modern power signal boxes. An operator requests a route from one signal to another, and the interlocking logic checks that every section is clear, every point is free to move, and no conflicting route is already active. Only when these conditions are met does the signalling system lock the route and clear the starting signal, authorizing the train driver to proceed. The locking mechanism is mechanical in older systems or electronic in modern ones, but the principle remains: a route once set cannot be dissolved until the train has passed through.

Variants and complexity

Routes can be simple, spanning perhaps two or three block sections on a single line, or complex, involving multiple points and crossings on a busy junction. Some systems allow routes to be set in advance and held until a train needs them, while others set them only when a train is ready to move. In busy yards and terminal areas, multiple short routes may be interlocked together so that setting one automatically prevents conflicting movements several platforms away. Timed route release is common: the signalling system automatically cancels a route after a set period if the train has not used it, freeing the sections for other traffic.

The term route emerged from the need to describe a complete, protected passage rather than individual signals or points. Unlike a signal, which governs one train movement, a route encompasses the entire locked corridor. Unlike a point, which is a single mechanical device, a route is an abstract construct enforced by the interlocking. In everyday railway language, operators speak of setting a route, holding a route, and clearing or cancelling a route, making it the fundamental unit of traffic control in signalled railways.

Where routes fail or conflict, trains cannot proceed safely, so route setting is one of the first things investigated in signal failures. Poor design of route interlocking logic can create deadlock situations where legitimate train movements are impossible without manually cancelling routes. Modern systems use computer-based interlocking to generate routes automatically in response to train detection and scheduling data, reducing manual intervention and speeding up traffic flow, but the route itself remains the core concept of how signalling grants permission for movement.