Why do speed limit signs usually say something about “speed checked by radar?” If the signs don’t have a warning and an officer uses radar and catches me speeding, can I have the case thrown out?
Probably not. It’s more or less a way of the municipality warning you that they do use radar, and may be watching you at any time in an effort to get you to slow down.
Basically what they’re saying is “We use radar to enforce speed limits…We can’t afford to have an officer posted here 24/7, so this sign will nag at the back of your mind that we could be watching you at any given time.”
My theory is that the vague warning of the signs “Speed enforced by radar”, around here, is intentional. By implying that there’s some sort of constant, hidden radaring going on (a la photo radar, for example), people may be more likely to curb their speed. The preponderance of these signs in places that never have actual radar going on (roads in residential areas, not on through streets, etc.) seems to make this scenario more likely.