High temperatures caused a "heat kink" along a stretch of Metrorail track, officials said, closing a portion of Green Line service throughout the weekend and likely impacting the Monday morning rush hour.
Service between Fort Totten and Prince George's Plaza was suspended Saturday and Sunday while crews repaired the 1,000-foot section of track bent out of shape because of the hot weather.
Metro officials announced Sunday night that service had restarted between the two stations, but trains were single-tracking. Crews planned to work Sunday night to rebuild 1,000 feet of track damaged in Friday's derailment near West Hyattsville Station, but were unsure if trains could operate as usual on Monday.
Metro advised people traveling on the Green Line to plan 15-20 minutes of additional travel time on Monday morning.
The late afternoon storm that swept through the area also delayed repairs, as crews cleared the repair site to take cover in safe areas, Metro spokesman Dan Stessel said.
Though the kink was only reported on the Green Line, all rail lines were affected by the problem. Officials imposed a 35 mph speed limit on all above-ground areas for every line through Sunday closing.
Scheduled track work was also suspended.
According to the transportation system, at about 4:45 p.m. on Friday, three cars on the inbound Green Line train came off the track as it entered a tunnel from an outdoor section. No injuries were reported.
Officials said that the high heat can make the rails expand, and when they expand farther than their cross-ties allow, the rail can move out of alignment. Mr. Stessel said there had been track inspectors out last week as a precaution during the hot weather.
Any time the temperature hits the upper 90s or above, especially when combined with direct sunlight, there are enhanced inspections.
"Track inspectors walk the tracks in between trains, looking for any signs of anomaly," he said.
This wasn't the first heat kink for the system, nor the only issue with bent or cracked rails this year.
In January, a 4-inch crack in a Yellow Line train was found near the Pentagon station just before the morning rush hour. Officials blamed the crack on freezing temperatures.
In 2010 and 2011 — the two hottest summers on record, according to the National Weather Service — kinks appeared in Red Line tracks.
Mr. Stessel said even though officials settled on a heat kink being the cause of Friday's derailment, before any steps can be taken for future prevention, other factors need to be examined.
"Out of that process, there will be recommendations for mitigating future occurrences like this," he said.
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