The oppressive heat affected man and machine Thursday.
The heat caused "track defects" on the Dan Ryan branch of the Red Line Thursday, which prompted delays during the evening rush. Trains had to operate on a single track between Cermak-Chinatown and Sox-35th.
That same area is currently designated a slow zone, with overnight repairs under way nearly every weeknight in the last few weeks.
But I haven't seen any similar missive about hot weather. Of course, Mother Nature attacked where the CTA is most vulnerable - in the slow zones.