Page 568 - IRSEM_Main Book

 These points are communicated to make the trains automatically and continuously adjust
their speed while maintaining the safety and comfort (jerk) requirements.

 So, the trains continuously receive information regarding the distance to the preceding
train and are then able to adjust their safety distance accordingly.

Moving Block principle

First, let us understand the conventional Fixed Block system as depicted in the first figure.

 The figure shows the total occupancy of the leading train by including the whole blocks
which the train is located on.

 This is due to the fact that it is impossible for the system to know exactly where the train
actually is within these blocks.

 Therefore, the fixed block system only allows the following train to move up to the last
unoccupied block's border.

Now, the Moving block is a significant refinement over the Fixed Block system.

 The train position and its braking curve is continuously calculated by the trains.

 Train then communicates its train position via radio to the wayside equipment.

 Thus, the wayside equipment is able to establish protected areas, each one called Limit of
Movement Authority (LMA), up to the nearest obstacle (in the figure the tail of the train
in front).

 Movement Authority (MA) is the permission for a train to move to a specific location
within the constraints of the infrastructure and with supervision of speed.

 Occupancy calculated in these systems must include a safety margin for location
uncertainty.

o It is depicted by the yellow lines in front and rear of the trains.

o It is called footprint.

o This safety margin depends on the accuracy of the odometry system in the train.

Annexure G3: CBTC in Metro Railway Systems Page 511 of 535