A train driver was absent for four minutes and became the culprit of a collapse that occurred in the Seoul subway in South Korea.
The subway employee went to the toilet and was gone for only 4 minutes and 16 seconds, but a lot happened during that time.
In the morning, the Seoul metro, like many other subways around the world, is rush hour. If you deviate from the schedule even for a couple of minutes, real chaos will begin, writes The Sun .

This is what happened when one train driver went to the toilet. When he returned 256 seconds later, he realized that he had caused a transport collapse.
There was a delay of almost half an hour during the morning rush hour. About 125 trains were behind schedule and resumed service with a delay of 15-20 minutes or more.
The situation was brought under control and the incident had almost no impact on the passengers, the publication notes.
For reference
The metro is an urban off-street railway with its own gauge.