they've been doing this kind of shit in texas for a couple of years now, usually in rural areas on two lane highways, like texas 80 north of nixon and alternate 90 west of Seguin. they will put up what looks like a road construction sign right before a blind curve, the sign will say "Road Survey Ahead."
shortly before you come upon that sign you will have seen a highway patrol car sitting in the opposite shoulder and thought to yourself, "he's gunna get somebody."
after rounding the curve you will see that they have the road pinched down and a line of cars waiting to get through. At the survey point there will be a law enforcement officer, his car will be parked with his lights flashing.
when you turn around to avoid the checkpoint the cop you saw before the sign will pull you over to ask why you turned around, "it wasn't to dodge the survey was it? is there anything in the vehicle you don't want them knowing about?"
:::voice of experience:::