Collisions may be within station section or in the block section. It may be
- Head on collision
- Head to tail collision or Rear collision
- Side collision
Collision in station section:
In station section, any of the above three types of collisions may occur.
Head on collision or Rear collision:
Any of the two may occur because of the wrong allocation of line or passing a signal at on by the loco pilot. In extreme exigencies equipment failure or unauthorized interference with the system may result in the signal coming OFF for an occupied line where flank protection is provided.
The yard may be equipped with:
- No track circuiting of berthing track in the yard.
- Mainline track circuited between fouling mark to fouling mark where loop lines are not track circuited.
- Entire yard track circuited.
In the first case where no track circuiting of berthing track is available observing clearance of line is to be done from the station, manually. In such a case any laxity in checking line clearance may result in the head on or head to a tail collision. Another situation may be where the loco pilot has passed the signal at ON. In both the situations, it is very difficult to find out the cause if the station staff takes a stand that the loco pilot has passed the signal at ON and the loco pilot says that he saw the signal OFF. The inference shall be drawn about the cause of the accident by the Train log records of the station and both the cabins along with their private number books, if taken into custody in time, the statements of the operating staff of the station and the loco pilot, assistant loco pilot and Guard of the affected train.
In the second case where mainline is track circuited while loop lines are not track circuited, the collision taking place on non-track circuited line shall lead to a similar situation as in the first case. However, in case, the collision occurs on track circuited line it shall not be possible to take OFF the signal for the occupied line and hence a train could not be received on the occupied line unless the track circuit had been bypassed. In this case, also inference can be drawn by observing the same procedure as in preceding paragraph, except that in this case the signal failure book, the presence of the signal maintainer at the station with specific reference to the relay room should be given additional cognizance.
In the case when the entire yard is track circuited usually in case of central panel interlocking or RRI, the system is such that it is not possible to receive a train on a track occupied besides unauthorized interference is almost impossible. The central panel interlocked stations are usually provided with data loggers which, when accounted for with other records and statements of staff it is possible to a large extent to substantiate the cause of the accident.
Side collision in station section:
Side collision may take place in Three situations:
- First when a train is standing on a line infringing with the schedule of dimensions with the adjoining line on a turnout or crossover.
- The other case when coaches or wagons of the derailed train are fouling with the adjoining track.
- In this case, when a train moves on the adjoining line infringed upon, as mentioned, shall collide by its side with the other train.
Side collision when the train is standing on a line infringing with the schedule of dimensions with the adjoining line on a turnout or crossover. The GR 4.56 provides that “When a train comes to a stand at a station, the Guard shall see that, whenever possible, the last vehicle of his train has cleared the fouling marks of all points and crossings. If not, he shall inform the station at once and exhibit Stop hand signal to prevent any movement on the fouled line”.
In addition, on stations where point zone is not track circuited, a fouling bar is provided linked with the point in such a way that it is not possible to change the position of the point from the last operating position unless the train clears the fouling bar. With this, it shall not be possible to receive next train on adjoining line unless the points are changed from their last operating position. On stations where point zones are track circuited flank protection is achieved by providing track circuits in such a way that the part of the track circuit falling within the fouling mark, if occupied shall not permit taking OFF the signal for adjoining line fouling the line on which train is already standing.
Side collision on the straight route: Side collision in station section on straight route shall be under similar circumstances as in case of side collision in the Block section.
Collision in the Block section:
Head on collision:
In block section, the head-on collision may take place on single line section or under special circumstances when single line working has been introduced on double line section due to any reason.In case of head-on collision on single line
- One of the possibility is disregard of ‘ON’ last stop signal at one of the station thereby two trains entering into the block section simultaneously from both ends
- Extraction of tokens at block stations at both ends of the block section.
- The erroneous issue of authority to pass the last stop signal at danger when the Block Instrument is defective or the Block Working has been suspended for any reason.
Head to tail collision or Rear collision:
In double line section due to:
- Disregard of the ‘ON’ last stop signal, in such as situation the collision may be averted if both the trains maintain equal speed and the leading train does not stop in the Block section.
- Erroneous issue of authority to pass the last stop signal at danger when a train is already in block section, when the Block Instrument is defective or the Block.
- Working has been suspended for any reason.