Continuity mistake: In one scene C. Thomas Howell almost runs head-on with an 18 wheeler, but just misses it. However, the truck clips the car he is driving and clearly takes the bumper clean off. The next driving scene shows the bumper back on the car.
Revealing mistake: When Jim hits the brakes in his stolen patrol car, the two pursuing police cars turn and flip over and over. As they roll, the 'roll cannon' is visible on the underside of one of the cars (a round steel tube in a hole in the floor) and at left, the two cannon slugs from both cars bounce down the road. This device fires the slug downward, and the force behind it lifts the car when the slug hits the road, launching the car over.
Answer: The windshield glass would have not broken this easily (like regular window pane glass in your home or such). I am going to guess that kind of glass hasn't been used on car windshields since at least the early 70's, if not before. The Sheriff's truck didn't appear to be that old, either.