I would guess that you do what you have to do on a hasty bugout, but I can see how an organized evacuation convoy would have a lot of use for some frequency jamming equipment on hand for isolating a particular checkpoint before busting through it.

The Army thinks so too:

http://www.army-technology.com/contractors/surveillance/scg/scg2.html

The rig in that picture would not shut down every form of comms in a given area, but five jammers hitting five frequencies is about right for shutting down local government tactical comms.