A high-visibility warning device carried by train crews and track workers to manually protect a train or a work zone. When displayed on or beside the track, it commands any approaching locomotive to stop immediately. By rule, a train cannot pass a red flag until the person who placed it gives explicit permission or physically removes it.
Heard on the job
The section gang has a red flag up at milepost 42, so we need to be prepared to stop short of their work limits.