Traffic radars use a beam of very high frequency waves (microwaves) that are concentrated in very narrow angles to improve detection and sensitivity. Generally speaking, it is like a beam of light emitted from the kinemometer (radar) that bounces off the vehicle. Depending on the speed of the vehicle, the wave will bounce back to the radar with different characteristics, making it possible to calculate the exact speed at which it was travelling when it passed through the beam emitted.
The nature of the “beam” makes it impossible for the radar to work both behind banks, corners or other elements that are opaque to the radio waves, and metals.
In the case of arch radars, you should know that these devices are capable of determining the lane of the vehicle that it is measuring.
The regular operating frequency is the well known Ka Band (from 34 to 36 GHz).
The emission strength of the radars is extremely low, especially in arches, so they are more complicated to detect.