Coming from 635 or 121 towards the north entrance of DFW, the speed limit drops from 65 to 50, then 1 mile later increases to 55, then in less than a mile, it drops to 40 before the toll gates at DFW. DFW police sit right under the overpass prior to the toll gates and nail people that haven’t slowed down from 55 to 40 soon enough. They will pull you over after you go through the booths and write you an expensive ticket. Depending on what part of the airport you are in, you will have to fight it in one of several different jurisdictions.