Page 565 - IRSEM_Main Book

Annexure: G-3

Communication Based Train Control (CBTC) in Metro Railway Systems

1 A centralized control is inescapable to monitor and handle any emergencies.

With closed doors to ensure passenger safety, there is a need for opening the train
doors on the correct side for the platform which has to be again failsafe to prevent
wrong side opening leading to passenger injury.

2 In order to achieve safety with a number of trains using the same line, it is essential
to provide information to the driver by some sort of “signals” about where to stop or
how fast the train can go etc.

3 To derive the information required to convey to the driver through “signals”, some
form of train detection was essential, to know where exactly the train in question is
with reference to other trains or other hurdles.

4 To provide means for more than one train to use the same line, it became necessary
to divide the line into “blocks” and ensure there is only one train in each “block”.

5 To control the trains and allow precedence between slow and fast trains, it became
necessary to have stations with turnouts and loops.

6 To ensure the points and crossings of a turnout were set within safety limits for
prevention of derailment, it was necessary to ‘detect’ the point by the signalling
system before allowing train movement i.e it was necessary to “interlock” the signal
with the points. The interlocking may be achieved through Relay based or
Microprocessor based.

7 Centralized Traffic control by a single operator controlling a line to avoid time delay
for exchange of information between Station Masters for increasing the line capacity
resulted in further advances such as block working, automatic Block signalling.

8 The rolling stock must have automatic train protection to eliminate driver errors.

9 The need for high frequency of train service necessitate automation of train
supervision and route setting for quick turn round in terminal stations.

10 In Communication Based Train Control (CBTC) signalling system, the primary train
detection is purely based on failsafe communication link between the train and the
control centre with the train communicating its position continuously and the
control centre communicates the position to other trains for maintain the safety
distance between two trains. Track circuits or axle counters if any are used only as a
secondary detection in case the Metro operator desires a fall back system.

11 Train Spacing and its Impact on Safety and Line Capacity (Headway):

Considering the need for higher order of safety, as well due to the presence of halts
at frequent intervals of even less than a KM length, Primarily the train detection is
done by communication, based on the train location, the movement of authority is
to be updated which is known as a moving block, which include a safety envelope
behind and in front of a train, always moving along with the train.

Annexure G3: CBTC in Metro Railway Systems Page 508 of 535