The March subway collision in Tokyo that killed five passengers and injured 63 others was caused by a combination of factors, including a wheel load imbalance and improperly ground rail surfaces, a Transport Ministry investigative panel concluded Thursday.

Upon receipt of the panel’s final report, the ministry plans to order all railways to keep wheel load imbalances to less than 10 percent, check and correct track distortions, properly grind rails and maintain the proper angle of wheel flanges.

The report also urges railways to install additional rerailing frogs where necessary.

The derailment, which killed five passengers and injured 63 others, took place at 9:01 a.m. on March 8 near Nakameguro Station on the Hibiya Line. The Teito Rapid Transit Authority operates the line and a network of subways in the capital.

The derailed car, the last in the train, sideswiped a train going in the opposite direction on a parallel track at a curve, peeling back the side of a packed commuter coach.

The ministry immediately launched the investigative committee, consisting of 11 railway scholars and experts, to determine the cause of the accident.

After repeated simulations, the panel concluded that the accident was caused by multiple factors, including a wheel load imbalance, increased friction between train wheels and tracks, and improperly ground rail surfaces.

An examination of all 320 Teito subway cars of the same type as the derailed train revealed a wheel load imbalance of 20 percent or more on 18 cars. One car had a load imbalance of 29 percent.

The deadly accident highlights the importance of railways sharing and utilizing information on past accidents.

According to the Transport Ministry, Tokyu Corp. is the only railway that routinely checks and maintains wheel loads, as recommended by the report.

Tokyu started the wheel load correction after analyzing the cause of a March 1986 derailment at Yokohama Station that injured no one but delayed 88,000 passengers.

Teito knew of Tokyu’s effort to check and correct wheel loads but had not taken such measures on its own trains, the Transport Ministry said.

“We feel that railways that have not been involved in an accident have not sufficiently reflected on accidents by other carriers in their safety measures,” the last section of the 107-page report says.

The ministry picks out and distributes information on only a limited number of accidents to railways. Last year, it offered information on only 16 cases to railways. About 1,000 accidents occur every year.

Ministry officials said they are now considering creating a database to disseminate information, as recommended by the report.

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