There is a toll on exiting the airport based on how long you have been in. Once inside the airport, you can park or go anywhere without requiring tickets (other than the lower cost lots).

I thought it was weird at first, but have come to like the ease of access. For example, if the security in 1 terminal is bad, I just get back in my car and drive to another one; costs me nothing more and there are no gates/tickets involved.