RAILWAY SIGNALS

Railway Signals

1)  A signal is a mechanical or electrical device erected beside a railway line to pass information          relating to the state of the line ahead to train/engine drivers .

 2)The driver interprets the signal's indication and acts accordingly.

 3)Typically, a signal might inform the driver of the speed at which the train may safely proceed or it    may instruct the driver to stop.

Applications and Positioning of Signals:-

Originally, signals displayed simple stop/proceed indications. As traffic density increased, this proved to be too limiting and refinements were added. One such refinement was the addition of distant signals on the approach to stop signals. The distant signal gave the driver warning that he was approaching a signal which might require a stop. This allowed for an overall increase in speed, since trains no longer had to stop on sudden warning.

 Signals are used because of followings:-

1)that the line ahead is clear (free of any obstruction) or blocked

2)that the driver has permission to proceed.

3)the points (also called switch or turnout in the US) are set correctly.

4)the state of the next signal.

5) the train orders are to be picked up by the crew

6)Signals have aspects and indications.

7)The aspect is the visual appearance of the signal

 8)The indication is the meaning

History Of Railway Signalling:-

1825: FIRST RAILWAY LINE FOR GOODS TRAFFIC WAS OPENED BETWEEN   

          DARLINGTON TO STOCKTON (U.K.) UNIFORMED MEN ON HORSES GUIDED THE               TRAIN   . 

1830 : FIRST PASSENGER TRAIN BETWEEN LIVERPOOL AND MANCHESTER              POLICEMAN WERE POSTED AT FIXED INTERVALS.

    1838 : POLICEMEN WERE REPLACED BY FIXED MECHANICAL SIGNALS

1853 :  FIRST TRAIN SERVICE INTRODUCED ON INDIAN RAILWAYS, SEMAPHORE          SIGNALS WERE USED  .

          

Mechanical Signals:-

1)Older forms of signal displayed their different aspects by their physical position.

2)The most common form of mechanical signal worldwide is the semaphore signal.

3)This comprises a pivoted arm or blade that can be inclined at different angles.

4) A horizontal arm is the most restrictive indication (for 'danger', 'caution', 'stop and proceed' or 'stop and stay' depending on the type of signal).

Auxiliary Warning Systems(AWS):-

1)Applies Brakes automatically in case Driver disregards a Red Signal

2)Regulates Train Speed to 15 KMPH on Yellow Aspect 

3)Controls Train speed on RED signal

(Available on WR (1987) & CR Suburban Sections on Mumbai).

Post Mounting:-

When a single track is involved, the signal is normally mounted on a post which displays the arm or signal head at some height above the track, in order to allow it to be seen at a distance. The signal is normally put on the engine driver's side of the track.

Gantry mounting:-

When multiple tracks are involved, or where space does not permit post mounting, other forms are found. In double track territory one may find two signals mounted side by side on a bracket which itself is mounted on a post

Ground Mounting:-

1)Such signals may be physically smaller (termed dwarf signals). Rapid transit systems commonly use nothing but dwarf signals due to the restricted space.

2)In some situations where there is insufficient room for a post or gantry, signals may be mounted at ground level. 

The Types Signalling Systems in Railways

1)Time Interval Method:-

* Trains are Spaced Over an length of a track in such a way that , if the first train stops, the following    train driver should be able to stop the train in sufficient distance without colliding with the first one.

*This type is used where traffic is less and weight of the trains are less.
*This Type of System cannot  be used in Passenger rails since weight and traffic is High

2)Space Interval Method

In this method of “Control Over Movement”, the length of the track is divided in to sections called Blocks. The Entry of a train in to the ‘Block’ is controlled in such a way that only when it is free, a train can be allowed to enter it. This means that between two consecutive trains , there is definite space interval.

Classification And Types and Signals

1)Open Characteristics  :-

it is sub divided into

• Detonating Signals
• Hand Signals
• Fixed Signals

2) Functional Characteristics:-

further sub divided into-

• Stop type signals 
• Warner Signals
• Shunting Signals
• coloured Light Signals

3) Location Characteristics:-

a) Reception Signals-

• Quoter Signals
•  Home Signals

b) Departure Signals-

• Starter signals
• Advance Starter Signals

4) Special Characteristics-

• Repeater or Co-acting Signals
• Routing Signals
• Calling Signals
• Point Indicator
• Modified lower quadrant semaphore Signal
• Miscellaneous Signals

Temporary signals are located as When train is required to stop and the restriction on track is to be kept for more than a day.

1)Temporary signals are located as follows:

•   Caution indication signal
•   Stop indication signal
•   Termination signal

When train is not required to stop and restriction on track is to be kept for more than a day.

    

2)Temporary signals are located as-

• Caution indication signal
• Speed indication signal
• Termination signals.