Driver error caused the C-Train derailment at the Tuscany LRT station last month, Calgary Transit director Doug Morgan said Thursday.

The train left the tracks at the end of the northwest line in the early-morning hours of Sept. 20. It caused extensive damage to the multi-milllion-dollar vehicle and seriously injured the driver, described as a woman in her early 60s who is a "senior operator" with Calgary Transit.

On the day of the incident, acting transit director Russell Davies said the C-Train operator had accelerated to full speed in the wrong direction, but it was unclear how or why that happened.

After investigators spoke briefly with the driver and collected evidence from the train's "black box" and nearby security camera footage, Morgan told reporters Thursday there's no other explanation for the crash other than a mistake by the operator.

"We can't come up with a reason why it happened; we just see that behaviour as what the probable cause of the incident was," he said.

No one else was injured in the crash.

The derailed C-Train was damaged at the front end, in particular, after it left the tracks and crashed through a fence. (Evelyne Asselin/CBC)

The driver is out of hospital, but continues to be on paid leave while she recovers from her injuries, Morgan said.

She has only been briefly interviewed and does not remember the incident, he added. Calgary Transit plans a more extensive interview with her later.

"As they recover we're hoping more information will come forward," Morgan said.

Morgan said he couldn't comment on whether the driver would be fired or subject to disciplinary action.

The train crashed through a fence at the end of the line. The Tuscany LRT station can be seen just behind it in this photo. (Evelyne Asselin/CBC)

There is no evidence the driver suffered a medical episode prior to the crash.

"The train has controls that, if there is ever an incident where a person passes out or has a seizure, that the train would stop and [apply] emergency braking right away," Morgan said.

"It can't coast on its own. It needs to be actively controlled by the operator."

Calgary Transit is in the process of buying new C-Train cars to replace aging ones and expand the service of four-car trains. Each new car costs about $3.2 million.