Need for Speed.

One thing that I've always wondered is, in movies, how do those guys drive those cars like that. For one thing, if I had any of those cars, it would not get touched. More importantly, however, I have yet to see a ramp on the side of the interstate. Furthermore, I am still quite puzzled by how a car can ramp off the back fender of another car and do a barrell roll in midair and then land on all fours (and by fours I mean wheels). I just wonder sometimes. I suppose the ramps only come out when cops are chasing behind you at 120 miles per hour...