The National Transportation Safety Board will investigate the deaths of two maintenance workers who were hit and killed by a Bay Area Rapid Transit train Saturday as they were conducting a track inspection.

Two federal investigators were on their way to San Francisco Saturday night, according to a tweet by the NTSB. The California Public Utilities Commission and BART will provide support during the investigation, a statement from transit officials said.

The BART employee and contract worker were investigating a possible dip in the track when they were struck and killed about 1:53 p.m. between the Walnut Creek and Pleasant Hill stations in the East Bay, according to BART officials. Their names were not immediately released. One was acting as a lookout while the other inspected the track, officials said.

There were a number of personnel on the train when it struck the employees, Paul Oversier, assistant general manager of operations said in a news conference Saturday. The train was returning from the Richmond yard after delivering cars graffitied in the Concord yard that needed cleaning, he said. A transit strike halted regular BART operations on Friday.

"This is a tragic day in BART's history," Grace Crunican, general manager of the public transit system, said in a statement released by BART. "The entire BART family is grieving."

The workers who were killed had "extensive experience" with freight and passenger trains, according to the statement.

“They understand the railroad, they understand how to work around moving trains,” Oversier said. “They were doing today what they have done 100 if not 1,000 other times in their career.”

The train was running in automatic mode with an "experienced operator" at the computer controls, officials said. BART officials did not otherwise say who was at the controls, but Associated Press reported that some trains were being moved by managers.

The two unions representing BART workers had warned of safety risks if managers were allowed to operate trains during the work stoppage.

"The managers may very well have been train operators at one time, but still it's a bit of a struggle to come up to speed on short notice," Des Patten, a spokesman for Service Employees International Union Local 1021, said in a phone interview.

A radio transmission captured the moments after the incident. The train operator said: "BART emergency! BART emergency to Central! We just struck some individuals (at a track location) ... Central be advised it may be BART employees." Later, he said: "Both are deceased and definitely BART employees."

Transit employees went on strike Friday after a week of marathon negotiations broke down over work rules, including length of the workday and when overtime pay should kick in. BART, the nation's fifth-largest transit system, carries about 400,000 round-trip passengers each workday.

SEIU Local 1021 and Amalgamated Transit Union Local 1555 put out a joint statement expressing their "deepest sympathies for the families of the individuals who died in this tragic accident."

ATU officials said their 900 workers would not be picketing Sunday out of respect for the victims and their families.

An official with AFSCME Local 3993 confirmed that one of the workers who died was a member of its union who crossed the picket line. The American Federation of State, County and Municipal Employees was not on strike but had urged its members to support the other two unions, said Patricia Schuchardt, president of Local 3993.

Schuchardt said the unions had raised the safety issues during the negotiations.

"It's a very unsafe situation the agency gambled with," Schuchardt said. "Had there not been a strike, there would have been a lot more safety precautions out there."

The strike, the second by BART workers in four months, produced traffic jams and frustration Friday, but officials predicted the worst was yet to come.

Transportation officials said they believed many workers telecommuted or took the day off but would be back to their desks Monday. A BART spokeswoman said the system was considering adding more charter buses, but they would accommodate only a fraction of the displaced riders. 

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