Human error probed in T crash

Investigators ruled out mechanical problems yesterday as the cause of the fatal commuter train crash in Woburn and are focusing on how human error put the Boston-bound train on a collision course with a work crew.

Two workers were killed and four were injured, while 10 passengers suffered minor injuries, as the train rammed the repair vehicle and ground to a halt Tuesday.

"We're focusing on several aspects of [the] human element, but there are several people that help operate a railroad," said Ted Turpin, lead investigator for the National Transportation Safety Board. He would not say whether the actions of more than one person were being investigated.

Federal investigators are trying to determine why a routine procedure to protect the work crew broke down, resulting in the crash. Earlier Tuesday, eight commuter trains passed the track repair work site without incident. But before the next train approached, a warning signal and a switch that would have diverted the train to another set of tracks were not set correctly.

An unidentified dispatcher in the rail system's Somerville control center, who has been placed on administrative leave, was overseeing the procedure. But investigators said they have not yet determined who might be at fault.

Rick Inclima, safety director for the repair workers union, said it appears the six-man work crew did everything they could to ensure their safety.

"Some problem with the dispatch center will prove to be the case," he said yesterday. "Clearly, the protections were in place. The work crew expected that train on the other track and had moved out of the way, and, lo and behold, the catastrophe happened."

Officials with the Brotherhood of Maintenance of Way Employees said the accident underscored safety problems in the MBTA commuter rail system since a private consortium started running it in 2003.

Federal records show that four worker fatalities, including the two Tuesday, have occurred on the 13-line system since the Massachusetts Bay Commuter Railroad began a $1.07 billion contract with the Massachusetts Bay Transportation Authority. In December 2003, a worker was struck and killed as he cleared snow at the Wellesley Farms station platform. In June 2006, a 36-year-old worker was crushed to death by track maintenance machinery in Gloucester.

In the preceding seven years, under Amtrak's control, only one worker was killed on the job, according to Federal Railroad Administration records, which do not go back further than 1996. In 1997, a train struck a work crew in Concord.

"We are sickened by this tragedy and appalled by the safety record of the MBCR," said Freddie Simpson, the union's president. "This is abhorrent and totally unacceptable."

A commuter rail spokesman said yesterday that the four deaths under MBCR management were unrelated and do not reflect a safety problem.

"MBCR has taken great pains to implement safety training programs, systems safeguards, and, in some cases, daily safety reminders for workers, " said spokesman Scott Farmelant. "But none of this will prevent human error."

The crash resulted from an extremely rare breakdown of a process that occurs almost daily: dispatchers routing trains around repair crews and other work sites.

Tuesday morning, the work crew was authorized to be on the inbound tracks to repair ties between Mishawum Station and the Montvale Avenue crossing in Woburn. The crew began work around 9 a.m., after the morning rush, and was scheduled to be there until 3 p.m., MBTA officials said.

There are two parallel sets of tracks, one for inbound trains to Boston, one for those outbound to Lowell. The dispatcher overseeing the Boston-Lowell line, who began work at 7 a.m. and was scheduled to leave at 3 p.m., kept outbound trains on their regular tracks. Inbound trains were routed around the workers by triggering a track switcher located about 3 miles north of the work site that moved them to the outbound tracks. Once the inbound trains were safely past the site, they were switched back to the inbound tracks by the dispatcher.

According to T officials, the switches north and south of the work site were toggled back and forth throughout the morning as four inbound trains made their runs around the work crew using the outbound tracks. While four outbound trains did not switch tracks, they were under the same speed restriction. Officials said there were no problems reported with the track signals or switching equipment.

But the dispatcher kept inbound train No. 322 on the inbound tracks through the work site, officials said. In addition, a red track signal, which alerts train crews to an occupied track and warns them to slow down, was switched to green, indicating that the track was clear and that there was no speed restriction, they said. Shortly before 2 p.m., the train barreled toward the unsuspecting work crew at close to the 60-mile-per-hour speed limit, officials said.

Asked if the investigation was focusing on the actions of the dispatcher, MBTA spokesman Joe Pesaturo said only that it remained an ongoing probe.

NTSB investigators plan to interview the dispatcher tomorrow. The dispatcher has been interviewed by other investigators, and, like everyone else involved, was being tested for drug and alcohol use, Turpin said. He said that he interviewed other workers in the dispatching center, the maintenance department, and their union representatives yesterday.

Investigators have also collected the digital records of each switch action from the Somerville dispatch center and have downloaded data from the locomotive to determine engine speed and torque, officials said.

Daniel can be reached at mdaniel@globe.com; Mishra at rmishra@globe.com.