OC Transpo says a broken switch and an operator’s failure to check for it caused last week’s partial O-Train derailment.

In a memo, OC Transpo general manager John Manconi said the switch at the Carleton University station, which moves to direct trains from one track to the other, didn’t properly close during the afternoon of Aug. 11.

The switch was broken when a train went over it, causing the switch to stay open and trigger a signal light problem, according to the memo.

Manconi said the light issue was reported to traffic control by the next train's driver, who slowed down according to Canadian Rail Operating Rules.

However, Manconi said the driver did not get out of the train and physically inspect the track before driving over that section, which caused the second and third train sections to derail.

He said they’ve taken "appropriate internal action" to make sure rules are being followed.

One person was taken to hospital with minor injuries because of the crash, which put the O-Train out of service until the next morning.

Manconi said they’re working to figure out why the switch didn’t properly close and what repairs or maintenance will have to be done to the train.