Teito Rapid Transit Authority on Friday denied media speculation that Wednesday's fatal subway collision was caused by the sliding of locked wheels, arguing that this situation would make a derailment unlikely.
"I am of the understanding that it has nothing to do with the derailment," Tadayoshi Tohama, director of the carrier's rolling stock department, told a news conference.
Friday's daily Yomiuri Shimbun reported on its front page that an expert working for the subway operator had written a thesis concluding that wheels often lock up and slide on curves similar to the one where Wednesday's accident occurred -- near Nakameguro Station on the Hibiya Line. The accident claimed four people's lives and injured 35 others.