One light rail car slammed into the back of another near the platform at the West Portal stations Saturday. Federal investigators arrived on scene Sunday morning. They have already determined that the breaks on the train were working just fine. They have one more mechanical issue to inspect, whether the track signals were working properly at the time of the crash.
The other possibility, investigators said Sunday, is driver error.
Inspectors continue to comb through the wreckage of one of the worst light rail accidents in San Francisco history. Muni's K-line car was pulled out of commission Saturday after the L-Taraval train slammed into it at the West Portal station.
The National Transportation Safety Board is now in charge of the investigation. Authorities want to know whether human error caused the crash.
"We've done the mechanical inspection. The post-accident test show that the breaks were working as intended," NTSB investigator Ted Turpin said.
Investigators also want to interview the driver, but he remains hospitalized with non-life threatening injuries, along with three others. 47 people in all were injured in the crash.
"Our deepest concerns go out to those individuals who were injured as well as their families. We do not take these situations lightly at all," said San Francico's MTA Executive Director Nat Ford.
Investigators say the train switched from automatic to manual mode while it was stopped in the tunnel, before it arrived at the platform. They say it would have been the driver who made that change. When the L-line slammed into the stationary K-train it was doing at least 20 miles per hour.
"However, the train should have been stopping at the station. Where the collision happened it should have been stopping, not doing 20 mph," Turpin told ABC7.
Few details are being released about the driver and his record. Investigators will not release his name. They will only say that he has driven a Muni bus since 1979 and the light rail trains since 2007.
Witnesses say he may have been asleep or unconscious just before the crash.
"He looked like he was asleep or passed out. I couldn't tell. But he was not looking at me," witness Nancy Martin told ABC7.
The driver has been tested for drugs and alcohol but the results of those tests are not in yet. Federal investigators say they will be in San Francisco for the next few days, but the results of the investigation could take anywhere from nine months to a year to complete.