Continuity mistake: When Rosco gets out of the car with the Detour sign, the arrow points to the right, the way Boss went. When he sets the sign up, it points left. Then after Luke grabs it and sets it out ahead of Jessie, it points back to the right.
Revealing mistake: When watching the film in the beginning, one of the cops pursuing Jessie and Boss rolls over. As he does so, you can see the roll bars in the car, which accounts for the car not crushing.