Excessive speed appears to have been the most direct cause. According to the Aircraft and Railway Accidents Investigation Commission, the train entered a sharp curve at a speed of 108 kph, far exceeding the set limit of 70 kph, and derailed, causing the carriages to crash into an apartment block. Track marks suggest that the driver applied the emergency breaks just before the curve. The commission has not yet concluded why the train entered the curve at this excessive speed.
However, a widely circulated presumption is that the driver, 23 years old with 11 months’ experience on the job, was trying to recover a 90-second delay following a 40-metre overrun at the previous station.
As for indirect causes, the failure of the company to instal the new Automatic Train Stop (ATS) system and guard rails in time is the most cited by many train experts. Most urban commuter trains in Japan now operate with ATS, which automatically decelerates the train if it exceeds the speed limit. Some busy lines are equipped with the even more advanced Automatic Train Control (ATC) system.
JR West had recognised the need for ATS on this line and at the time of the accident was planning to install the system. During rush hours, trains operate every four to five minutes. The number of trains on the line, as well as their speed, have increased since privatisation.
This increase was made in order to compete with another private railway line running nearly parallel to the JR West line. Having failed to make necessary safety investments prior to such an increase, the company cannot expect to avoid being blamed for putting profit before safety.