Depends really on the area and workload for the police - if their workload is light, they might undertake "stationary RBT" where they setup roadside and pull cars in. This requires the room to stop vehicles without disrupting traffic, and also requires adequate lightint for night time operations (OH&S). Stationary RBT will also not be undertaken in adverse weather (again, OH&S, not because the cops don't want to get wet, more to do with stepping out in front of moving vehicles in reduced visibility can be hazardous to one's health).

There is also "mobile RBT", where the cops drive around and happen to pull over for a breath test anyone they happen to find themselves behind.

HTH.

Dave