The speed you'll drive is the product of innumerable in-born and external influences (which include past experience). Laws would be useless if people had free will, actually. They work because of a deterrent effect; getting pulled over paying fines, and maybe going to jail feels bad. It's the threat of feeling bad that makes laws an effective incentive, and we can't change that emotional response.
If humans had free will, though, we could decide how we emotionally react to anything. We could decide to flip a switch in our minds so that jail is emotionally fulfilling and preferable to freedom. Then there'd be no way to punish anybody, and thus we could have no laws.
Can you decide that you'll enjoy cutting off one of your fingers? If so, it seems silly not to, since you'll enjoy it!