This can be obtained with pretty much any character, though it's easier with a muscle character like The Hulk or The Thing. As muscle, simply run around town and slam into cars, then keep hitting
to destroy them. It's entirely possible to destroy them just by ramming them enough times.
As anyone else, stand in the middle of a lane and keep doing a ranged attack to destroy incoming cars. If they stop coming, run off in search of more cars.