Metro officials say they're working on new guidelines for operating in periods of extreme heat.

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The transit system also says it'll improve emergency practices and procedures by speeding up response times.

The discussion at a meeting Thursday followed two separate incidents in Prince George's County last week: a partial derailment along the green line, and an evacuation three days earlier that occurred when a train lost power.

In that incident, many stranded passengers who had been waiting on the train exited the cars and walked along the tracks.

The derailment, which led to the emergency evacuation of dozens of passengers, has been blamed on a so-called "heat kink" that bent a stretch of track out of shape.