The Tsurumi rail accident occurred on the morning of 9 November 1963 between Tsurumi Station and Shin-Koyasu Station on the Tōkaidō Main Line in Yokohama, Japan. A freight train, hauled by a JNR Class EF15 electric locomotive, was traveling on the down freight line when the 43rd wagon derailed. Two following wagons overturned and obstructed the adjacent up passenger line, setting the stage for a catastrophic collision.

Shortly after the derailment, a 12-car electric multiple unit passenger train bound for Tokyo collided with the derailed freight wagons. The front three carriages of this train derailed and struck the side of a second 12-carriage passenger train traveling on the down passenger line toward Kurihama. The multiple collisions resulted in 162 fatalities and 120 injuries, making it one of the deadliest railway accidents in Japanese history.

Investigations by Japanese National Railways initially found that the freight train’s speed, approximately 60 km/h, was not excessive and that no obvious faults were present in the track or rolling stock. A more detailed study by the Railway Technical Research Institute from 1967 to 1972 determined that the derailment resulted from a combination of wheelset design, rail cross-section and wear, and track geometry. These factors together caused instability that led to the derailment of the freight wagons.

In response to the accident, Japanese National Railways introduced dynamic track-inspection cars and enhanced monitoring of track conditions to prevent similar disasters. The Tsurumi accident remains the second deadliest rail disaster in Japan, prompting major improvements in rail safety practices, derailment prevention, and track maintenance procedures that continue to influence railway operations to this day.