Well, you have provided no context whatsoever, but presumably in #1, the person spoken to is either driving now or scheduled to do so, but the speaker doesn't believe it. #2 seems simply to ban the person spoken to from operating the vehicle, or to observe that s/he does not have the skill to do so.
New words, one handy idiom, and a 2-minute quiz — delivered to your inbox to keep your streak alive.