Our town recently got one of those Traffic Speed Detecting Signs, that
tell you how fast you're going. I've always wondered how they work, and
why they dont detect cars going the opposite direction.(I assume they
work on radar). I also noticed that they only have TWO digits.
Therefore, if you exceed 99mph, what does the sign do?

Last night I was in a convenvience store, when one of the local cops
walked in. That was my chance to ask him what happens if someone exceeds
99mph. His reply was "I'll give you a speeding ticket". I laughed and
said "that's what I thought you'd say". Then I said, "besides the
ticket, what would the sign do?" He said he never tried it, so he dont
know.

If a cop dont know, who does? I'm wondering if they go back to zero, or
just keep showing 99?????