1. Some lapses in Employee alertness. It is difficult for detecting some mishaps and some problems some where in the middle of stations and far away from either side. Lapses in Ensuring only one train being on one track.
2. Fire accidents or track displacement due to some terrorist attacks using bombs.
3. Old worn out parts and devices - used in train engines coaches, and traction.
Damage of tracks due to cyclones etc.
4. Improper periodic maintenance of tracks and other systems involved in traction and
in trains - engines and coaches. If there is any negligence. Usually it does not happen.
5. Over speeding in curves.
6. Failure of Collision avoidance systems, train presence detection systems on railway tracks.
There are other automatic systems to alert in case of alarming situation. If these do not work due to some reason, there could be a problem.