The distance from the stop signal to the clearing point is the overlap (also overrun, or clearing distance).
The overlap is usually about 400m or so with lower-quadrant or 2-aspect signalling, and 180m with modified lower-quadrant, upper-quadrant, or MACL signalling where warners or distants protect the approach to the stop signal.
Derailing switches or points to sand humps, sidings, etc., can also be interlocked (see below) so that they are automatically set to isolate the line when signals are taken off for the adjacent line.
Haye's Derails (which guide the flanges of wheels over and across to the outer side of the rails to derail a moving vehicle), Scotch Blocks (which prevent points from being set for vehicles on the loop line to be sent to the main line), and similar devices are sometimes used (more so in the past - these are less common now).
More commonly now, derailing switches (points that deliberately take the moving vehicle off the line and derail them) or points that lead to sand humps or sidings are used.
All normal operations of running the trains -- accelerating them, braking them, etc., are handled by the ATO system, with speeds up to 80km/h. Around Chennai, several suburban stations have their signals automatically controllable from Basin Bridge using a fault-tolerant system that interconnects the signalling of up to 32 stations using a dual fibre-optic ring.
This system also provides for 6 voice channels for communication among these stations.
AWS (Automatic Warning System) is an in-cab signal warning system, is used in suburban EMU systems, primarily Mumbai.
It was proposed for main lines including New Delhi - Agra, Howrah - Mughalsarai, etc.Some sections still use different forms of physical token systems such as the Neale's Ball Token instruments.Other than the block system some other special-purpose methods of train working are used in some circumstances.No trains may be parked to the rear of the clearing point on the track protected by the stop signal.This provides a margin of safety in case a train overshoots a stop signal which is on, because of brake failure, driver inattention, etc.The clearing point is the point ahead of a stop signal up to which the track must be kept clear of obstructions in order for a train to be accepted from the rear of the signal.