A Washington, DC, Metro train broke down for unknown reasons and another one jumped the tracks in another routine day for DC rail transit. The derailment was caused by a “heat kink” in the tracks, and Metro says it normally slows down trains during “extreme heat,” but hadn’t decided to do so in this heat wave.
Metal expands when it gets warm, and railroads used to leave gaps between the rails every 35 feet or so to allow for such expansion. But modern railroads weld the rails together to form a continuous ribbon that is prone to kinking at high temperatures. To deal with this, they use special allows that, they hope, won’t buckle in hot weather. The alloys used on Metro rails are good to temperatures up to 95 degrees, which DC exceeded for 11 days straight. Apparently, no one at Metro remembered to issue the slow orders.