Reader Lisa Koh wrote in to ask: "On what occasion will the passengers be allowed to leave the MRT (train) if the breakdown happens in the tunnel?"
She said people would fear being stuck on the train for long periods.
Transport reporter Adrian Lim answered.
Trains can stall in a tunnel for several reasons, including power faults and signalling issues.
If power from the tracks is disrupted, there is a backup battery on the train which can last for 60 minutes. The battery keeps lights and the ventilation system going.
If the train service cannot be restored, guidelines state that detrainment should occur within 30 minutes of an incident, if it is safe to do so.
During detrainment, power along the rail tracks is shut down for safety.
The Singapore Civil Defence Force will also be on site to assist passengers, to walk to the nearest MRT station via the tracks.
Detrainment, however, is not always the best option.
Depending on which section of the tracks the train stalls at, it could mean a considerable walk to the nearest MRT station.
It would thus be preferable to ferry commuters to the nearest station, for example, by either driving the problematic train manually (if the trains are driverless), or to do a push-out, which is to use another train to push the stalled train to the nearest station.
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