SANTA ANA (AP)  -- A Southern California commuter train that sideswiped a freight train on Thursday had run a red signal, and officials are looking at brake problems or human error as possible causes.

No serious injuries were reported in the accident in Rialto, but the episode stirred still-vivid memories of the deadly September train collision in Chatsworth between a Metrolink commuter train and a freight train.

New safety procedures were put in place after that crash, which killed 25 people and was attributed to the failure of a Metrolink engineer to stop at a red light so an oncoming Union Pacific train could go by.

The eastbound Metrolink train in Thursday's incident was carrying 15 passengers and crew members and failed to stop at a red light about 150 feet from where it hit the rear cars of a westbound BNSF freight train, said Ted Turpin, an investigator for the National Transportation Safety Board.

Turpin said Friday that the four-car Metrolink train had nearly stopped and that the red signal appeared to have been working. Two engineers on the Metrolink train took note of yellow signals earlier on the route, he said, but the train didn't stop before the BNSF freight had eased onto a side track.

``They were attempting to stop the train,'' Turpin told The Associated Press. ``This Metrolink train was trying to stop and missed.''

Turpin said the effort to brake marks a key difference between this incident and September's deadly crash, in which investigators found no indication the brakes were applied.

In Thursday's incident, investigators are looking at the brakes and the train's operators as they try to determine the cause, he said.

``We're focusing on braking and human factors and performance,'' Turpin said.

Francisco Oaxaca, a spokesman for Metrolink, declined to comment.

Four people were taken to the hospital with minor injuries after the crash in Rialto, about 60 miles east of downtown Los Angeles.