What happens in a signalbox?

A number of levers are provided, numbered sequentially from the left, each operating a signal, point, facing point lock (or another function). The levers are coloured to show their function (red is a stop signal, black is a point, blue is a facing point lock, yellow is a distant signal, blue plus black is a motorised point and FPL, red plus brown is an interlocking lever giving a release to another box). A plate on the lever shows the number of that lever and (if there is space to do so) describes its function and lists the other levers that have to be pulled in sequence to release it. Where the lever is electrically locked (in addition to the mechanical locking provided) then an electrical plunger may be fitted just above the lever. Alternatively (at Arley and for some levers at Bewdley South and Kidderminster for example) electrical locking may be effected by a circuit controller which operates the electric lock as the lever is moved.

The location of the points and signals is shown on a track diagram above the lever frame, which may also contain lamps to indicate (when lit) that a train or vehicles is standing on a particular section of track. These lamps are driven by track circuits and the occupation of track circuits may be used as part of the electrical locking. Where signals cannot be seen from the box, then a repeater on the block shelf provides confirmation that the signal has responded correctly to the lever - in this simulation, repeaters are not currently provided.

Trains may only be despatched on the 'absolute block' system after communication on the bells with an adjacent signalbox - the signal giving permission for trains to leave 'station limits' is normally provided with an electric lock which can only be released from the box in advance. To signify this the lever has a white stripe. A train register is provided in which all bell signals are recorded, giving the beats on the bell, the running line, the direction and the time. Each message has a unique combimation of beats on the bell and each bell (one for each pair of running lines) has a unique tone. Exeter West has six block bells, as there are six pairs of running lines (Main lines in each direction, Southern, Middle, Goods and Relief).

Interlocking between the levers ensures that conflicting routes cannot be set, signals can only be cleared if the route is set and the route cannot be disturbed while the signals are 'OFF', i.e. cleared. The interlocking is effected in three ways - mechanically through the lever frame, electrically through electric locks on the lever and mechanically remote from the signal box.

All of this is accurately simulated in this application.