Paceline has nothing to do with road closures.

Riders form a paceline because of the crosswind which forces everyone to look for draft on the left or the right side of a rider in front of you. Eventually, there's not enough road for everyone to be in the draft and the first paceline is formed (also called an echelon).

More specifically though, paceline refers to the mechanics of the echelon, the way riders rotate, or take turns at the front to stay in the echelon. This rotation is the paceline.