There are no federal laws for that. That is "policy" and handled at the state or local level depending on the type of roadblock.

>Roadblocks still fall under regulations. For example, every third car.
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>As for airports, it's pretty much all done by computers now, which means no humans making most of the decsions. I've been pulled for random search before, but it was long ago, before no-fly lists and computer selection.
>
>>That is only true in most circumstances (Like to search you or your vehicle and I even think it is possible that the anti-terrorism laws made loopholes around that one). For example, if they setup a road block to stop all drivers for dui or seatbelt violations, they can indeed stop you on a whim and ask to see your drivers license, registration, and even give you the "test." :o)
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>>In airports you can be selected for security scanning as well. It used to be "random" but supposedly now it is more geared towards intelligence information (which is scary).