Roadblocks in the US are not at all common but in a SHTF scenario, they happen. Look at the roadblocks around the New Orleans area for instance. And shelters for the displaced.
All had authority figures who believed their job was not to ensure just treatment but simply to ensure peace and quiet. To pass their inspection you have to present no threat nor give them any reason to think you are anything but another refugee.
Someone who looks paramilitary will get special attention.

But then again, a DPM kilt might get you a bye on the the search for weapons. Or it'll just go a lot faster :-)

unimogbert