|At first the most important thing to say that "A Driver of a train shall not start his train until he is authorised to do so". To give authority to the driver to start, signal posts have been erected at various places to indicate him whether to start or not. The driver shall not pass a signal unless he sees it has been TAKEN OFF i.e. Signal turned to either GREEN, or TWO YELLOW or ONE YELLOW. If the Signal is at ON position, i.e. RED, he must not pass it unless he is authorised to pass on a Written Authority issued by the Station Master. (This is done in case of Signal Failures).
There are certain circumstances in which although signal is RED, yet written authority is not required. For example GATE SIGNAL, INTERMEDIATE BLOCK STOP SIGNAL, AUTOMATIC SIGNAL.
To ensure a train shall proceed safely from one station to other there are various SYSTEMS of WORKING adopted in Indian Railways. The system adopted depends upon the density of traffic, i.e. more the number of trains the more costly the system adopted. Among this system, any one is followed for running of trains between two station. These systems are:
1. ABSOLUTE BLOCK SYSTEM
2. AUTOMATIC BLOCK STSTEM
3. FOLLOWING TRAIN STSTEM
4. PILOT GUARD SYSTEM
5. TRAIN STAFF TICKETING SYSTEM
6. ONE TRAIN ONLY SYSTEM
ABSOLUTE BLOCK SYSTEM
AUTOMATIC BLOCK SYSTEM
This system is improvement over the Absolute Block System. In this a block section between two block station is further sub-divided into different block signalling section. Which means where one train can run between two block station in Absolute Block System, there more number of train can run in between two block stations.
ASPECTS OF AUTOMATIC SIGNALS
Sequence of Change of Signals with respect to running train in Automatic Block System
In Automatic Block System, each signals convey the aspect of next Signal(s) to the driver. For example, if a signal is ONE-YELLOW, it tells the driver that the next signal is RED. If it is DOUBLE-YELLOW, then next signal is DOUBLE-YELLOW or ONE-YELLOW, and if it is GREEN, then next signal is either GREEN or DOUBLE-YELLOW.
Each signals telling the driver the aspects of next (few) signals helps the driver to run the train at more speed and helps him to control the speed when required.