Picking up on SMO’s high school physics concept – which makes perfect sense, except that it requires someone standing there with a stopwatch and then everyone else believing them – a fairly simple security camera with a time code on its display would not only provide the measurement of the speed but the evidence of the offence.
If you also have a by-law in place, it would certainly give your committee the grounds on which to issue a Notice To Comply (or whatever the equivalent is in your state).
That’s assuming, of course, that the speeder wasn’t on the EC.