At least here in Maryland, cops sometimes set up stationary speed checkpoints either in the median or on the shoulder of major highways. The configuration often has one or two patrol cars parked with their trunk/hood open (to obscure the light bars), and a couple of cops hiding out with a radar or lidar gun. When they spot someone they want to ticket, the usual tactic is for one cop to step into the roadway and vigorously wave the car over. Frankly its scary to watch, especially with the way some people drive around here.
There is usually a backup unit further down the road, in case the suspect doesn't stop for the guys on foot.
