Human error may have caused the collision of two trains in western Japan Tuesday that killed 42 and injured 500, investigators say.

The engineer of a West Japan Railway express train from Kyoto said he was given a green light to proceed on a track where the other train was stopped.The local rail company in Minaguchi may have let its train go onto the single-line track 10 minutes later than scheduled after a delay caused by a signal failure, putting the train in the path of the express train, Hiroshi Saiki of the Transport Ministry explained.

The engineer of the express, Mitsuaki Hayashi, who miraculously survived the crash, told the Kyodo News Service that the signal should have been red but was green.

"An employee of the Shigaraki railway gave a green signal to the train even though an automated signal was showing red," police inspector Takeharu Yamamoto said.

A West Japan Railway spokesman said there was no way to contact the driver of the special express train to alert him that the local train was not running on schedule. He said the local train should have waited in the previous station for the express train, which was running on schedule, to pass.

But an unidentified official of the Shigaraki Railway said the express line failed to follow certain unspecified safety procedures.