This video puts some perspective on the action-movie high-speed car chase jump phenomenon. Notice how close this car comes to wrecking when launched off of a little teeny two-foot-high ramp and moving at a relatively slow velocity.
In fact, just for fun, let's do a rough estimate of the takeoff velocity. We approximate that the car lands about 10 meters from its takeoff point and is in the air for close to one second. Applying this information we can do a simple calculation to determine its horizontal component of velocity on takeoff:
vx = Δx/ t = 10 m/1s = 10 m/s
Using a little vector addition we can also determine the net velocity off the ramp based on the ramp angle. We'll leave this as an exercise for anyone so inclined (no pun intended), but because the take off angle is pretty small (we estimated 17 degrees) the net velocity is still only approximately 10.5 m/s or 23 mi/hr -- not really a high-speed stunt.
Fun, games and calculations aside, one of many problems any "would-be" stunt car driver is going to face on attempting a jump, is that the car is generally going to follow the standard parabolic trajectory of a projectile.