How is the common "interval speed measurement" on the expressway measured?

Interval speed measurement means that there are two cameras at the beginning and end of the road. From the first shot to the last shot, the interval distance is fixed, so the distance divided by the time equals the speed. Some interval speedometers will also be equipped with radar to measure the speed when you take pictures. Radar velocity measurement is the Doppler effect mentioned above. Judging your car by radar reflection, all radar speed measurement on the market is narrow-wave radar, so it is aimed at electronic dogs. There is no problem with the constant speed measurement. The electronic dog can detect it. See for yourself. If it's moving speed measurement, you can't see it yourself, but if it's speeding, the electronic dog can't detect it.