Several people are arrested on grounds of subversive activity and given the choice between going to prison and trying to escape their sentences by participating in a race against time in a desert known as Punishment Park.
This is social science fiction. It doesn't specify whether it takes place in the near future or in an alternate universe (Nixon is still portrayed as being the president), but I suspect that it isn't really supposed to matter. In fact, since the whole thing is very convincingly shot as a documentary, it may well be that the makers were hoping that it would mistaken for one. Ultimately, though I admire the craft of making this look convincing, it's also obvious and predictable once you figure out that it's fiction-with-a-message; knowing this type of movie, you should be able to figure out just how many of the participants in the race regain their freedom. And the endless arguments between the counterculturists/revolutionaries and the members of the establishment do get tiresome after a while. It's powerful enough, but as always, one should consider the nature of film-making and remind themselves that it is a piece of fiction before they decide what lessons they wish to glean from it.