Metro implemented speed restrictions Tuesday afternoon because of an increased risk of heat-warped tracks, causing delays through rush hour, into the evening and possibly into Wednesday as temperatures climb. Trains traveled no faster than 35 mph on aboveground sections of the system as a preventive measure after the Green Line derailment July 6. That train was traveling faster than 50 mph when it hit a heat kink near West Hyattsville Station causing three cars to derail. Speed restrictions enable a train to stop more quickly if another heat kink develops. A train operating without heat restrictions runs at about 55 mph between aboveground stations, Metro spokesman Phillip Stewart said. Despite the slowed train speeds, passengers were not delayed more than five to 10 minutes, Mr. Stewart said. The speed restriction was lifted at 6:30 p.m. Tuesday. A heat kink develops when the steel rails reach temperatures above 135 degrees and release pressure by popping sideways. During any period with sustained weather in the mid- to high 90s, extra rail inspectors walk the 106-mile system with infrared guns to measure rail temperatures and look for abnormalities.
