BOSTON (AP) – Federal investigators on Thursday checked trackside signals – as well as reports a trolley driver may have been on a cell phone – as they sought to determine the cause of a collision between two trains in suburban Newton that killed the driver and injured more than a dozen passengers.

The crash killed Terrese Edmonds, 24, who was operating a two-car train that rammed the back of the other two-car train about 6 p.m. Wednesday.

National Transportation Safety Board member Kitty Higgins said the signals were being examined because the T’s Green Line trains are run manually and guided by so-called “wayside” signals.

The train that was rammed Wednesday night had just begun to move after being stopped at a red light on an outbound track just outside the Woodland Station in suburban Newton.

Passengers, meanwhile, reported seeing Edmonds on the phone in the moments before the collision.

“I heard something about that but we don’t know yet,” Higgins told reporters during the NTSB’s first on-site briefing. “We’re just beginning to look at this; we’ll look at everything.”

Higgins said rail investigator Wayne Workman and his team would assess equipment, human performance and safety systems. In particular, they planned to interview operators of the train that was struck, the surviving crewman in the trolley that rammed it and supervisors at the T’s command center, which can track the speed and location of equipment.

The first interviews were slated for Friday.

“We will find our what caused the accident by looking at all the various factors that I’ve mentioned,” Higgins said barely four hours after flying up from Washington.

Edmonds was a relatively inexperienced trolley operator who was hired last August and began commanding a train in October. She was a part-time employee like most new hires.

“She waited for a long time, a couple of years, for the job and she finally got it. She was so happy,” said her brother Leon.

Operators must be high school graduates, hold a driver’s license, complete background checks and undergo a seven-week training program that includes classroom work and trolley driving.

The train that was rammed was later removed from the scene, but the one that caused the collision remained so it could be examined, according to Joe Pesaturo, spokesman for the Massachusetts Bay Transportation Authority. Passengers were bused around the site on Thursday.

More than one-third of the roof was bent downward over the cab where Edmonds had been working. For roughly seven hours, firefighters struggled frantically to free her from the mangled wreckage before her body was extricated early Thursday morning.

“I was able to look at the damage to the car; it was very severe,” Higgins said.

The collision also seriously injured a passenger who was flown by helicopter to the Boston Medical Center. Nine others were treated at Newton-Wellesley Hospital and about five were treated at the scene, Pesaturo said.

A woman who called 911 from her home near the tracks immediately after the crash can be heard shouting to injured passengers, but got no response.

“The T is on fire and there are people hurt,” she told the dispatcher in tapes released Thursday. “Wow, it’s bad.”

AP-ES-05-29-08 1546EDT