Crackdown

In addition to andrew's solution at a 3 and 4 star rating you have to run over 3 gang members to fill a bar of driving experience but even after a 4 star rating a back flip (or any trick) with the agency SUV will still give you close to a full bar. So I suggest going down to the southern Los Muertos beach and jumping with the SUV off the lifegaurd towers till it falls apart then press start and extract to a supply point and get another SUV. You'll be looking at 120-140 jumps as opposed to killing 300-400 guys.

If you're going for 1000 then you might want to get all the hidden orbs and then jump through all of the unique stunt rings first and then you'll see how much grinding is actually required since both of these will give you experience towards driving and both have achievements attached to them.