Every morning, we passed in single file through a narrow, black, wrought-iron gate in the six-foot-high stone wall which separated the school from the chaos on the Falls Road.

Source: https://www.irishcentral.com/culture/eimear-ocallaghans-diary-belfast-troubles

In Antakya, lots of of excavators stuffed dump vehicles which moved on in single file as operations to search out survivors wound down.

Source: https://basquiatstrings.co.uk/pollution-fears-over-turkey-quake-waste-bt-news

Students are reminded to board a school bus in single file and wait on the sidewalk until the bus has come to a complete stop.

Source: https://ntv.ca/rnc-focused-on-back-to-school-traffic-safety-awareness-2/