Roadblocks serve a variety of purposes. Some of them are: Keeping an area inaccessible to outside persons, creating a bottleneck to impede traffic, to create points of inspection (looking for wanted persons, persons of interest, contraband, etc), and another is containment. If a roadblock is successfully planned, and setup, it will be hard to circumvent. Ideally, a road block will allow no means to bypass it. Setting up a roadblock on a major interstate can be done, but it will not be easy. A one lane or two lane road is ideal. I do not plan on very much travel in a post balloon popping world, but I do foresee roadblocks in at least 3 points. During the evacuations of the Gulf cities, we saw massive lines of people moving north. One local genius wearing a badge decided he needed to setup a roadblock. Why I will never know, but I STRONGLY suspect he and his brother-in-law profited immensely from it as it was positioned right beyond the biggest gas station/convenience store in town. I think we will see police and military roadblocks for a long time after a massive SHTF, but in the event it is THE SHTF, people had better watch for roadblocks by armed thugs.