The agency says the accident was caused at least in part by two equipment problems: uneven wear on the tracks and flawed maintenance on a train wheel. BART safety investigators say the problems are "red flags" that likely contributed to the derailment.
The accident happened between the Pleasant Hill and Pittsburg/Bay Point stations. The two cars that derailed remained upright, but three passengers were taken to the hospital with neck pain. The accident disrupted BART service for hours.
BART says it has addressed the equipment problems. It has called in experts from the Transportation Technology Center to conduct an independent investigation.