After Tim shoots Chick, he jumps into the car, puts it in gear and drives off. But he never turns on the engine. He had just finished putting the injured guy into the front passenger's seat of the car when Chick came out, so he hadn't yet turned on the engine. The crew obviously had started the engine for the convenience of the production.
(At about 10:20) When Tim runs his car into the "roadside", the ground visibly bounces: obviously a cushioned stop.