NEWTON - Federal investigators began scouring the mangled metal from Wednesday night's fatal MBTA crash yesterday, probing whether the rear-end crash was caused by human error, broken track signals, flaws in the rail, or some other unknown problem.
Eleven investigators from the National Transportation Safety Board immediately began taking measurements at the wooded crash scene and requesting records that could show how fast the train that instigated the crash was moving, and where its cars were in the moments leading up to the crash, said Kitty Higgins, an NTSB member who came to Newton to work on the investigation.
The NTSB also plans to pursue the cellphone records of Terrese Edmonds, the deceased operator of the second train at the time of the crash, one official said. Massachusetts Bay Transportation Authority regulations ban vehicle operators from using cellphones while driving, T officials confirmed yesterday.
While authorities offered no indication that Edmonds was on her cellphone, Higgins responded to reporters' inquiries at a morning briefing by saying: "I just heard that somebody said there was a cellphone. . . . That's part of the information that's out there. I don't know if it's accurate. Our investigators have not interviewed anybody, but it's one of the things we look at in every investigation."
Investigators, beginning today, plan to start interviewing passengers and employees at the T's operations center, which dispatches trolleys, she said.
As they ask questions about the crash, investigators will have to contend with an antiquated subway line that depended heavily on the reactions of a rookie operator who had been running a trolley for six months following a seven-week training course. The operator had been a part-time employee for most of that time, according to her father, Terry Jones.
The MBTA declined to release Edmonds's full personnel file, but Steve MacDougall, president of her union, said she was considered a "model employee" by her peers.
The trolley does not have a standard "black box," similar to those in airplanes, that reveals precise actions of the operator and records conversations, but it probably has recorded data on the movements of the car wheels at the time of the crash, Higgins said.
The 5:55 p.m. crash, which involved one moving Green Line train (a pair of articulated trolley cars) rear-ending a second train that had just begun to move, left the 24-year-old Edmonds dead and at least seven passengers injured. The trains were carrying a combined 180 to 200 passengers, Higgins said.
"The impact was significant," she said. "The front of the car was pushed in."
The front train was removed from the tracks early yesterday morning. Most of the focus was on the second train, the one that was moving and hit the first train. The second train remained on the tracks yesterday, disrupting the D Branch of the Green Line. Officials were hoping to restore full service today.
Higgins said investigators are also looking at wayside signals, a set of traffic lights on the side of the tracks that lets drivers know when it is safe to go and stop.
But investigators have yet to determine the trolley's speed or whether the brakes were applied before the crash, she said. Green Line trolleys are allowed to go as fast as 40 miles per hour in the area of the crash, between the Waban and Woodland stations on the D Branch.
A final report on the crash, which would also include recommendations to prevent similar accidents around the country, could take as long as 18 months.
The Green Line is a 19th-century antique and the oldest line in the MBTA, which is the country's oldest subway system. It has been under scrutiny for years because of numerous crashes and derailments.
In the 1990s, after several incidents, the American Public Transit Association produced a report with 17 safety recommendations for the Green Line. A rear-end crash in 1995 at Copley Station left 32 people injured.
Unlike other lines, the Green Line does not have a fail-safe computer system that disables trains that slip past red lights.
Instead, it relies on radio contact between operator and dispatcher and strict rules intended to keep trolleys from running into each other.
"There's nothing to prevent them from going through a red light," said Bob Moses, who retired last year after dispatching all four lines on the MBTA over more than two decades.
Moses said he mostly avoided working the Green Line. "I prefer dispatching the other lines," he said. "It's safer, and that's what the bottom line is. We don't have a permanent good signal system on the Green Line."
Moving trolley cars are supposed to stay 500 feet apart. In most instances, they must stay 100 feet behind stopped trolleys. Trolley operators are supposed to stop at all red signals.
When a signal appears broken or there is a question, operators are allowed to contact radio dispatchers and ask for permission to move slowly ahead, after waiting 60 seconds. But the driver is ultimately responsible for controlling the speed of the train.
The requirements for running the complicated trolley cars are spare. Operators are required to be at least 18 years old, to have been driving a car at least three years, and have a high school diploma or its equivalent, under MBTA rules.
Following seven weeks of training, including classroom and field experience, they must pass a test with questions about signals, switches, safety rules, and defensive driving techniques, MBTA spokesman Joe Pesaturo said.
If they pass, they spend three days with an experienced operator. After another day in the classroom, they are on their own.
In New York City, train operators undergo about three months of training to drive one of the 6,300 cars in its 26-line system, said Charles Seaton, a spokesman for the Metropolitan Transportation Authority in New York City.
Those who drive lettered lines in New York City receive 114 days of training, and those who operate trains on numbered lines get 80 days of training.
Seaton said the lettered lines require more training because operators have to learn how to use more equipment.
David Abel, Michael Levenson, Martin Finucane, James Vaznis, and John R. Ellement of the Globe staff and Globe correspondents Matt Collette and Kate Augusto contributed to this report. Noah Bierman can be reached at email@example.com.