They cannot physically stop every car on the road and ask for a license or ask if you have drugs/illegal stuff in the car without probable cause. What they are really looking for is someone to make an illegal U-Turn or exit the road off the shoulder which gives them the right to really stop you. All they can do is slow you down and look for illegal items that are in plain sight.
Guam does this on holidays. They set a radar trap and stop everyone who is even slightly over the speed limit. (Hint they will tell you you were over the limit whether you were or not)If you have no open beer or are not chewing betel nut they then let you go without a ticket.
What you have described on a road would be analogous to having and ICE agent stand beside the door of the bus and look at everyone who is boarding. Yeah, obnoxious but legal.
The police do not have the right to stop everyone and ask for ID. They cannot enter a bus and ask everyone for ID.
They can and do within the border areas. Travel on I-10 near TX/NM. There is a border patrol checkpoint that stops all traffic.
Not allowed to chew betel nut in Guam?