Surely they cant measure speed as the wheelbase of different vehicles is very different.What happens when an artic crosses them, bump bump bump bump bump bump
A pair of detector ropes can tell them the number of axles crossing, their direction of travel and their speed. They can also determine the wheelbase of the vehicle so have a good idea how many vehicles passing are motorcycles.As for the purpose of a succession of them, it might be to log the buildup of traffic jams or to count how many people head off to use “rat-runs” through residential ares or to find out where people tend to speed.