Speed Monitored by Aircraft?

What Does that even MEAN? How are they going to monitor my speed with their helicopter and pull me over with the car, and how often do they actually do that? I bet they did it once so they could put that cool sign there. It reminds me of fast and the furious or Gone in 60 seconds where the Nic Cage steals the car and then outruns the helicopter in it! That was intense, or just movie magic, but thats enough procrastinating, time to work on exams....