A one under is the grim radio and breakroom shorthand for a pedestrian or trespasser being struck by a locomotive and ending up beneath the rolling stock. These incidents trigger immediate emergency protocols, halt all traffic on the affected lines, and mandate trauma leave for the train crew.
Heard on the job
Dispatch, we just had a one under at the grade crossing, get emergency services rolling immediately.
Insider tip
This is a somber, strictly internal term used by crews to quickly communicate a traumatic incident without broadcasting graphic details over open radio channels.