An automated train operated by Yokohama Seaside Line Company near Tokyo went into reverse, injuring 14 passengers.
Police say the train moved backward for about 25 meters before coming into contact with a buffer at the terminal station, Shin-Sugita, shortly after 8 p.m. on Saturday. About 30 people were on board the train at the time.
The driverless trains run on a guideway under control from headquarters. The company says three people were monitoring and controlling the operation at the time of the accident.
But they reportedly were unable to notice that the train had shifted into reverse, and became aware of an abnormal situation only when the collision triggered an emergency stop.
The president of the operating company apologized for the accident at a news conference.
Akihiko Mikami said the trains are just not supposed to run in reverse.