BART said in a press release Wednesday that at 8:45 a.m. Monday, the computer system that monitors and manages BART tracks experienced a localized loss in communication with a field device specific to an area near the Orinda station, including the track interlocking located between the Orinda and Lafayette stations.
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The transit agency said when this occurs, its operations control center doesn't receive a status indication of route alignments in the area and track positions cannot be controlled remotely.
The computer and communication system fails in a safe mode, for which there are procedures to continue train service while crews troubleshoot the loss of computer communication.
BART said the system was operating at the start of revenue service and one train already traveled east through the area.
At 8:50 a.m., BART's operation control center instructed the train operator of an approaching eight-car Antioch-bound train to manually align the route at the interlocking. The route was to be straight through.
BART said the train operator left the cab to align the track route. PA announcements were made to riders on the train about the delay. The train operator then confirmed with the control center the track was set for a straight through alignment. The control center instructed them to drive the train in manual mode through the area.
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Once the train was moving, BART said the train operator told the control center the train was crossing over to the opposite track, which was not the correct alignment.
The control center responded by holding all trains in the area and told the train operator to move from the Antioch end of the train to the SFO end of the train and to move the train in the SFO direction to clear the interlocking area of the track and correctly align the route for straight through movement.
The train operator walked to the other end of the train and moved it in manual mode in the SFO direction. That's when two cars derailed at a slow speed, causing electrical arcing, smoke, and flames.
BART said some riders immediately started to self-evacuate by using the emergency door release.
At 9:05 a.m., the train operator reported to the control center he believed the train derailed. The operator then walked through the train, telling people to evacuate. The operator also reported the smoke and flames to the control center and said people had already started evacuating.
MORE: 9 hospitalized after BART train derails and catches fire in East Bay, officials say
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BART said Orinda police were first to arrive on scene and helped evacuate all riders safely and firefighters extinguished the fire.
BART said by 9:23 a.m., the control center was told all riders on board -- which BART estimated to be about 100-150 people -- were already safely evacuated from the train.
That section of track where the derailment occurred, including the interlocking, was recently replaced and was in good operating order, BART officials said Wednesday. The system's train control system is being modernized as part of implementing Communications Based Train Control, a major rebuilding project underway.
BART said its investigation into the derailment continues. The transit agency has 60 calendar days from Monday to provide a report to the California Public Utilities Commission. Until the CPUC accepts and closes the report, the incident is considered "under investigation" and won't be available to the public.
Read full report here.