History's John Grabowski on the origins of standardized time zones

Clocks fall back. Daylight Saving Time ends this weekend

Signal Cleveland: John Grabowski, the Krieger-Mueller Joint Professor in History, explained that railroads revolutionized timekeeping in the 19th century, since they “could not work effectively or safely” when nearby communities each set clocks by their own sunrise and sunset—spurring the creation of standardized time zones and eventually Daylight Saving Time.