BOSTON -- Massachusetts Bay Transportation Authority trains were running again through Government Center Monday morning, but investigators are still trying to talk to the driver involved Friday's trolley collision.

Forty-six passengers were hurt when a Green Line MBTA trolley hit another car when the driver ran a red light while texting his girlfriend.

Three of four trolley cars were crushed and damages from the crash are estimated at $9.6 million.

Federal investigators said over the weekend that there was no mechanical problems that caused the crash. They said the operator not only ran a red light, but also passed a yellow light before the collision.

"Then the train encountered a yellow signal and a red signal. The point of collision occurred 80 feet past the red signal," NTSB board member Debbie Hersman said.

The driver of the second trolley, Aiden Quinn, 24, of Attleboro, Mass., may face criminal charges in the crash. Quinn will be fired later this week if investigators verify that he was using his cellular phone before the crash, MBTA General Manager Daniel Grabauskas said.

Quinn did not show up for a scheduled meeting with supervisors on Sunday, MBTA officials said.

Quinn’s car was traveling 25 mph when it careened into the back of the waiting train, officials said. It is unclear whether Quinn was braking immediately before the collision, but if the trolley’s speed was constant, the idling train would have been visible for at least 13 seconds before it was struck.

Investigators said that Quinn’s trolley also failed to stop at a red signal light 80 feet before the spot where the trolleys collided. The first trolley was pushed 31 feet down the tracks after it was struck.

NTSB officials said that rear lights from the waiting train should have been seen in the dark tunnel 480 feet from the spot where it was struck.

Trolley operators were already banned from texting, but Friday’s crash near Government Center has triggered an even tougher new policy that will soon take effect: If train drivers are caught with a cell phone while working, they will be fired.

Boston Carmen’s Union president Stephen Macdougall said the preventable accident does not reflect the behavior of most MBTA workers.

“The individual involved in last night’s incident and the issues led up to that tragedy were avoidable,” he said. “This was an individual act by an individual who does not represent the attitudes or the professional conduct of all or most MBTA workers.”

If Quinn was texting his girlfriend, he would be at least the 10th driver guilty of the offense in the last year.

In the last year, the transit agency has suspended at least nine other bus and trolley drivers for texting or talking on their cell phones while driving.