(CNN) -- An out-of-service Bay Area Rapid Transit train struck and killed two workers on a section of track northeast of San Francisco on Saturday afternoon, the transit authority said.
The employees were making track inspections near the Walnut Creek station, BART said in a statement. One was an employee and the other a contractor. Their names were not immediately released.
"Our hearts and prayers go out to the families of the two workers who've just been killed on the BART tracks," BART General Manager Grace Crunican said.
She said the accident is under investigation.
Paul Oversier, BART's head of operations, told reporters that the two workers were looking into a possible slight dip in the rail when they were hit.
The four-car train was on a routine maintenance run with an experienced operator at the controls, but at the time of the incident, it was being run in automatic mode under computer control, BART said.
The cars were being moved back to a train yard after having been cleaned of graffiti, Oversier said.
There were a number of other personnel on the train at the time, but officials have not had an opportunity to speak with them, Oversier said.
All train cabs are equipped with video cameras.
Victims were experienced employees, BART says
The victims had extensive experience working around moving trains, the transit authority said. The procedures involved in track maintenance require one employee to inspect the track and the other employee to act as a lookout for any oncoming traffic, it said.
They were supposed to stay clear of the track and be able to clear the operating area within 15 seconds of a train reaching them, Oversier said.
BART's union workers are currently on strike over a variety of issues, including wages. Oversier would not answer questions related to the strike, saying those issues were not at the forefront Saturday evening.
He did say the BART employee who was killed was a member of American Federation of State, County and Municipal Employees, one of the striking unions, adding only that the man "chose to come to work."
Another of the striking unions, Amalgamated Transit Union Local 1555, said it would not picket Sunday out of respect for the victims' families.
"This is a tragedy of the greatest proportions for the BART family," Oversier said.
Saturday was the second day of the strike that has paralyzed the San Francisco area. BART workers went on strike for four days in the summer over the same issues.
The BART system normally serves 26 communities, including San Francisco and Oakland. It has chartered buses during the strike, but those help only a fraction of the roughly 400,000 people who use the service each day.