Periodically I see a cable, or sometimes two, laying across the road for cars to drive over. What are these for? My only thoughts are that they either measure car speeds or count the number or cars that pass by. Why is there sometimes one cable and sometimes two? And what is the data used for? Thanks!
They qualify some street improvements for grants. That’s usually secondary to the traffic planning, signal phasing, and future road building that are the main reason that the counts are made, but I’m not in Traffic Section, so I’m not involved with that. Also, the traffic index and the % of trucks determines how thick the road needs to be. And comparing past counts lets you predict future traffic volumes.
Interestingly they work on air. When a car rolls over the tube air is compressed and the ticker-counter increases.
You can disconnect the tube at the end and blow through it causing the counter to increase, making it seem like a well traveled road. Then the county will give your street a fresh coat of pavement.
Same idea as the rubber hoses that gas stations used to use to ring a bell when someone drove up - back when they had service. They count traffic. If the counter is smart, hey can even get time-related traffic stats.
I have seen some city maps that give a relaive idea of how travelled most main streets are. Sometimes the measure is to see if road improvements are needed, sometimes just to update their statistics about traffic patterns.