Speed Monitored By Aircraft

I always pass these signs on long open stretches. "Speed Monitored By Aircraft" I am very confused as to how they do this. I've read many posts and lots of information about radar, and I still don't get how a moving plane can get an accurate speed reading of a car. Isn't that cosine effect thing going to be a major factor here? I never see planes buzzing the highway to be in a direct line with the direction of travel of a car. What gives?

Hi,

There are two main answers to this question:

1) Airplanes have much cooler radar systems that police cars. They are capable of far more that your average Police Radar Gun. An extreme example of this is an AWACS. Of course, an AWACS has more important things to worry about than a speeding car.

2) VASCAR. Instead of using a standard Police Radar Gun they can measure the amount of time it takes for you to drive from one point to another. VASCAR is basically a computer and a stopwatch connected together. Ever notice those big white stripes painted on the highway? You can bet that those are spaced at a specific (known) distance that is easy for a computer to calculate your speed by drive time. That distance is programmed into the computer. A person then starts the stopwatch when you pass the first stripe and then stops the stopwatch as you pass the second stripe down the road. The computer then takes that time and calculates your speed. If you're speeding, the aircraft can then radio your vehicle and speed to a trooper on the ground. This is undetectable by a radar detector, since there are no transmissions from the unit.

Hope this helps.