A Bay Area Rapid Transit train derailed last week after scalding-hot tracks warped rail lines out of alignment, BART said. Built for heat up to 115°F, the rails hit 140°F last Tuesday. Extreme heat has blanketed much of the U.S. over the past weeks, with tens of millions under heat advisories.. The East Bay derailment appears to be unprecedented — an agency spokesperson could not conclusively declare no train had ever derailed because of heat in the past, but a search of news archives found nothing since at least 2005. (San Francisco Chronicle $, LA Times $; Climate Signals background: Extreme heat and heatwaves)