BART officials said that an initial assessment of Tuesday's partial train derailment in Concord showed that heat played the "main role" in the event after excessive temperatures caused a curve in the track.
Approximately 50 passengers were safely evacuated when the 10-car train derailed near Hastings Drive and David Avenue, Contra Costa Fire reported at 6:27 p.m.
A small number of passengers reported minor injuries, Con Fire said.
Con Fire was on the scene to extinguish spot fires.
Due to the downed BART service between Pleasant Hill and Concord, Contra Costa County buses numbers 11 and 14 were made available between Pleasant Hill and Concord stations and were accepting BART tickets as fare, a spokesperson for BART said.
BART reps said that it would remained closed Tuesday evening between Pleasant Hill and Concord but they anticipated returning to single-tracking at a minimum on Wednesday.
Crews were set to remain through the night to remove the train and then cut out the damaged track and replace it, BART said.