The radar speed sign LED display size should be determined based on the traffic speed of the road where the radar speed sign will be located. Radarsign offers speed sign models in three LED display sizes.
Radar Speed Sign Viewing Chart
The chart below indicates the viewing distance for various LED digit heights. For example, starting at a distance of 600 feet from the radar speed sign at a speed of 45 mph you have 9.1 seconds to view a sign with 13″ LED display. That is ideal for that speed. However, at 75 mph you have only 5.4 seconds to view the sign which is not acceptable.