I think you need to sit him down and have a serious conversation with him where you assure him that you understand his reasons for not wanting you to smoke and drive. Tell him you respect him, his rules, and trust his judgment. You hope he trusts and respects you as well, and you wouldn't do something stupid to endanger your relationship. Then tell him that testing you every couple of weeks sends the message that he doesn't really trust you to adhere to the rules he set in regards to driving and it is in direct opposition to the message he gives by allowing you to grow. If you sit and calmly discuss this with him in an intelligent and mature manner, he may reconsider.