On a more serious note, something would have to be done about accurate measurement of these lower speeds. The capacity for error in measuring with radar guns and the like rises sharply below about 35 mph, even a minute shift of the gun can cause a very large shift in reading.
Following with a car won't help either, since car speedos have poor accuracy at lower speeds.
Back to old method of following for a set distance could work with a police officer also on a bike with one of our more accurate computer speedos. Raises an interesting image though:
"Good morning Sir, puff pant, I've been following you, puff pant, for one fifth of a mile, puff pant, at 27 mph in a restricted, puff pant, area, puff pant!
One for the camera phone.
