[Politically Correct]

Along with what you said about the real trap at the next exit, such checkpoints also rely on video cameras with powerful zoom lenses, often located on a highway overpass ahead of the bogus “drug search” sign. They are observing cars through the front windshield for sudden activity, including tossing anything out of a window.

Nah, not interested in what could be tossed from a window.
They're after the 10-100 Kilo runs.

[Travis McGee]

I think you are naive about that. Sure, they’d like to catch a 10-100 kilo load, but that is like finding a needle in a million haystacks. All they need is “probable cause” to stop John Q Citizen and toss his car. If they find so much as an old pot pipe, they own you. Or cash, such as for a cash-only auction. They’ll just take the cash. Or a firearm that is not kosher in that jurisdiction. Bingo, they own you again. They do this all the time. “Policing for profit.”