They typically have two vehicles, one vehicle has the load, and the other vehicle is totally clean.
They hire ordinary people with clean records to drive. The vehicle with the load leads the way and the clean vehicle stays a ways back.
If the first vehicle with the load gets pulled over the second vehicle comes up and does something crazy like a drunk driver would (goes on and off the road, buzzes the cop, anything to appear dangerous and out of control). At that point usually the cop will leave the first car and start pursuit of the second car instead. I say “usually”