Metro officials have revised their criteria for determining when to slow train speeds during periods of extreme heat.

Fort Totten station after a recent Green Line derailment. (Steven Logan)

Officials said Tuesday that if inspectors determine rail temperatures are higher than 135 degrees, operators may be asked to slow trains to 35 miles per hour. Other criteria may also prompt a slowdown, including prolonged heat waves of three days or more — much like the one that the region experienced earlier this month.

Whether Metro will impose heat restrictions Tuesday remains to be seen. According to the Capital Weather Gang, temperatures are expected to be in the high 90’s and may even cross the 100 degree mark.

Metro officials believe excessive heat was a factor in the derailment of a Green Line train on July 6. It derailed just outside of the West Hyattsville station after a “heat kink” developed in the track. There were no heat restrictions in place at the time, but officials immediately imposed them following the accident.

Metro’s General Manager Richard Sarles said that slowing trains during heatwaves may help prevent derailments because drivers could potentially spot track irregularities earlier and take steps to stop trains.