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Operator error — specifically, going too fast — was the cause of Sunday's TRAX derailment in South Salt Lake that injured three people, Utah Transit Authority officials said Wednesday.

"This was an apparent mistake by the operator. ... Excessive speed going into the curve," said Dave Goeres, UTA's chief safety and security officer.

The curve, just south of the Central Pointe TRAX Station, near 2100 South and 200 West, is rated at 15 mph.

But the TRAX driver was going 37 mph, Goeres said, according to an analysis of video and a data recorder on the train.

A safety factor is built into such curves to allow them to be taken faster than the rated speed, but "37 mph is too fast," Goeres said.

The driver, he added, is an "experienced" operator who had taken that curve many times while on the way to West Valley City.

Now that the safety review is completed, the driver — who was placed on administrative leave — will undergo a personnel review process, which could result in his being fired.

UTA spokesman Remi Barron said the personnel review will give the driver an opportunity to state a case for why the accident was not his fault.

Barron on Wednesday also addressed reports that the driver had appeared "angry" before the crash.

After reviewing video, both before and after the crash, "there doesn't appear there was any anger before or after," Barron said.

"He was 'upset,' was the term I heard," Barron said.

Goeres called the derailment a "one-off, unfortunate mistake, and that UTA continues to train its drivers to ensure they are familiar with all operational rules.

He said State Safety Oversight, which is the representative for the Federal Transit Administration, took part in the investigation.

UTA used cranes and other heavy equipment Monday to remove the train from where it left the tracks.

In all, 11 of the 14 people aboard were checked by paramedics Sunday, and three were transported to the hospital for treatment of minor injuries, Barron said.