can't figure out a movie (post-apocalyptic a la PANIC IN YEAR ZERO)

I have tried for a long time to figure out a movie that I watched twenty years ago. The movie was done in the seventies and it is about a group of people (a family? friends?) who flee a big town because of some terrible accident (nuclear? biologic?). On their way to a refuge in the countryside, they are constantly attacked by outlaws who take advantage of the disarray in which the society has fallen following the accident. No, I am not talking about Ray Milland's PANIC IN THE YEAR ZERO. It is a very similar story, but was done at least ten years after. Does it ring a bell? Does anyboby know the name of that movie? Thanks, Patrice.