Is it possibly linked to a fear of being in a situation where you don't have control over anything? If you do get pulled over for something minor broken tail light or something that you didn't even know about, you are not really in control of your life anymore, at least until he/she lets you go, with/with out a ticket.

I know that air travel causes me a lot of anxiety because once you walk past the ticket counter you are really at the mercy of the airlines until you get to your destination whenever that might be.