SACRAMENTO  (AP) — An investigation was underway Friday to determine why a Sacramento light rail commuter train struck a maintenance train, injuring 27 people.

The accident occurred around 9:40 p.m. Thursday and was initially believed to be a derailment, but Sacramento Regional Transit spokeswoman Devra Selenis confirmed Friday that it was a crash.

The maintenance train was not moving at the time, Selenis said in an email to The Associated Press.

“It’s currently under investigation to determine the cause,” she said.

There were 24 people on the Blue Line passenger train and three on the maintenance train.

Thirteen people were taken to hospitals, one with moderate injuries and 12 with minor injuries, Selenis said.

Sacramento Fire Department spokesman Keith Wade said 14 other people were treated at the scene and released.

“We’re very happy that no one lost their life and that no one was in critical condition,” Wade told reporters late Thursday.

The National Transportation Safety Board said it was sending a six-person team to investigate the crash.

The crash occurred in a dark and isolated area.

Nearby resident Anthony Hernandez told CBS Sacramento he heard the collision while he was putting his kids to bed.

“It rattled the houses,” Hernandez said.

Buses were being used Friday to carry rail passengers around the accident site.

The Blue Line is part of Sacramento Regional Transit’s 43-mile (69-kilometer), 52-station light rail system. Weekday light rail ridership averages about 40,000, according to the agency.