Lever frame

Mechanical railway signalling installations rely on lever frames for their operation to interlock the signals and points to allow the safe operation of trains in the area the signals control. Located in the signal box, the levers are operated by the signalman.

Overview

By the movement of individual levers, signals, points, level crossing gates or barriers and sometimes movable bridges over waterways are operated via wires and rods. The signaller chooses the correct combination of points, facing point locks and signals to operate, which will control the movement of each train through his or her area of control.

The lever frame contains interlocking designed to ensure that the levers cannot be operated to create a conflicting train movement. Each interlocking installation is individual and unique to the location controlled. The interlocking may be achieved mechanically or by electric lever locks, or (more usually) a combination of both.

Signals or points located some distance away from the signal box are sometimes electrically rather than mechanically operated. Movement of the controlling lever operates an electrical circuit controller. In the UK, it is practice to cut short the handles of any levers controlling electrical apparatus, to remind signalmen that little effort is required to move them.