How do you suppose to track the road?? Install beacons on the road? or are you trying to image process the whole road and find out the track???
Both methods are not easy. But the first method is costly but less complex in implementation.
Anyway, put a timer device for the steering and the brake.. If both were not used above a certain threshold, either the road is straight and no obstacles or the driver is sleeping!!! Even if the road is clear, the driver may feel boring and sleepy. So in both cases, you'd need to alert the driver. Hope I'm not speaking rubbish
Use an embedded controller or a single board computer rather than putting a huge PC in the car. That way you'd make it look like a real doable thing rather than a stupid model.