railroad

Interlocking and routing

The first attempts at interlocking switches and signals were made in France in 1855 and in Britain in 1856. Interlocking at crossings and junctions prevents the displaying of a clear signal for one route when clearance has already been given to a train on a conflicting route. Route-setting or route-interlocking systems are modern extensions of this principle. With them the signaling operator or dispatcher can set up a complete route through a complicated track area by simply pushing buttons on a control panel. Most interlockings employ electrical relays, but adoption of computer-based solid-state interlocking began in Europe and Japan in the 1980s. Safeguard against malfunction is obtained by duplication or triplication; parallel computer systems are arranged to examine electronic route-setting commands in different ways, and only if automatic comparison shows no discrepancy in their proof that conflicting routes have been secured will the apparatus set the required route.

Electronics have greatly widened the scope for precise but at the same time labour-saving control of a busy railroad’s traffic by making it possible to oversee extensive areas from one signaling or dispatching centre. This development is widely known as centralized traffic control (CTC). In Britain, ... (200 of 20,774 words)