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How vehicle counters that time to time we see on the road work ?

Discussion in 'Hobby Electronics' started by Guest, Jan 8, 2005.

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  1. Guest

    Guest Guest

    I'm sure you all see from time to time, some sort of device chained to a
    pole with a pair of road-wide cable or hose like sensor.I'm not sure bot I
    beleive they are vehicle counters (are they?) to collect data statistical
    analysis of the traffic.

    Do you know anything about them? If they are vehicle counters do you know
    how they work? What they use as sensor? How accurate they are? Can they
    distinguish different type of vehicles (caes, trucks etc) ? Can they detect
    mutiple vehicles passing over their cabe/hose simultaneously ?

  2. Caliban

    Caliban Guest

    I assume they work on a pneumatic to electric transducer (when the
    hollow cable is squashed the pressure inside increases and a count is
    produced). The count would be referenced to a clock to determine the
    volume of traffic v's time of day. This data could then be used to plan
    works involving disruption to traffic flow, and aid in road planning.

    I'd be interested in knowing if the versions with two cables spaced a
    short distance apart are be able to determine direction as well as
    volume of traffic (which sensor fires first), and possibly wheelbase
    length and speed (time for front wheels to cross both sensors combined
    with time for back wheels to cross both sensors). I've never seen these
    types extend across more than one lane.
  3. Dingo

    Dingo Guest

    I assume the cable is a switch that gets switched when a heavy enough load
    "squeezes" the cable enough.

    I'd imagine once a vehicle passes over it it has a timer of something like 1
    second before it will register another car. This way the back tyres are not
    counted as another car, or a semi-trailer as serveral cars.

    Just my guess.
  4. Only had a play with the very old versions.
    The ond one I had seen (a long time ago) was a pneumatic air pressures sensor
    that sensed quick air pressure changes. The pulses were divided by two, then
    that passed onto a mechanical counter.
    Geeze I'm a hoard. I still have the sensor.

    A StreeterAmet "Electronic Air Switch" from Measurement Systems Division.

    A cylindrical object about 40mm in diameter, with a piezo disk on one side,
    with three screw mount connectors on the other. Two for power, one for output.
    It outputs one short pulse per air pulse that comes in. The other side is
    mounted via hoses and such to the rubber hose that runs along the width of the
    With this model, since it is fixed to divide by two, reliability with cars
    would be excellent. Once you get trucks and such, it would throw the averages out.
    This one can't,
    I don't think any system would be able to tell, however:

    From what I've observed more recently, there can be two tubes across two lane
    roads (with one tube only the width of one lane), that way, there is more
    accurate counting even with multiple simultaineous vehicles on both lanes.

    As far as potential goes, two tubes spaced by a short distance, it could also
    give speed estimates.

    If you do away with rubber hoses, and use innductive loops, you can also
    indicate moving/stalled traffic.

    If they use a micro (which nowadays they would most likely), you can log
    traffic density at different times of day, with careful timing, they could
    count cars AND trucks (assuming a minimum time between vehicles), approx speed
    of those vehicles at those times, and whether or not the traffic was part of a
    parking lot or the traffic was moving.
  5. Richard

    Richard Guest

    As far as I know, they use a pressure transducer to give some idea of
    vehicle weight, ie bigger tyre - more pressure.

    Single strip measures counts only.

    Double strip senses counts, speed and direction. Every time you speed over
    one of these, the statistics gathered go in the favour of lowering speed

    Software is used to determine (to some degree) the type of vehicle from the
    raw data gathered.

    That's the limit of my knowledge. Perhaps someone who works for a traffic
    authority (ie Main Roads Perth) can shed more light.

    Had one in front of our house a few months ago. The first night some vandals
    cut the tubes. (Mindless idiots!) A week later the device was set up again
    and survived. The nuisance was the noise as vehicles passed over at all
    hours of the night! And the fact that tax payers' money was wasted in
    repairs and the whole excercise of data gathering had to be repeated.

  6. David Sauer

    David Sauer Guest

    They're used privately too.

    Had one outside a shopping centre being constructed. A few weeks later
    they had some advertising up about how xyz number of cars pass by this
  7. Rod Out back

    Rod Out back Guest


    A few years ago, the local council put one on the single-lane bitumen road
    through the creek channels near our homestead (shire road). We encouraged
    them to put it elsewhere, as the wet season was looming, and their location
    was right in the middle of the flood zone. However, they didnt listen to
    mere mortals...It was one of the old pneumatic tube systems, and I see they
    still use the same to date(they work and are easy to relocate).

    A fresh-faced young council official turns up after the creeks have been
    flooding for a fortnight, and now receeded. He asked if we had been and
    checked the counter recently (they had kindly left us a key to the box), and
    if there had been much traffic recorded. It was worthwhile to see his face
    when we told him it had switched from cars per day to litres per minute when
    the flood got to it a fortnight ago...

    They apparently found a freshwater crab residing in it when the box was
    opened. It tried to bite the council official...


    Rod.......Out Back
  8. Martin

    Martin Guest


    What a classic!!!
  9. Dingo

    Dingo Guest

    Snap Snap - Take that useless council!

    I wish a Fresh Water Crab would crawl into the envolope I pay my rates in ;)

  10. Albm&ctd

    Albm&ctd Guest

    On the contrary. If the number of cars passing are not doing anywhere
    near the speed limit that gives the sloths an indication that the
    current limit is too high.
    I suspect in this area a number of sneaky placements (for instance
    after roadwork signs) have resulted in false data (or collected data
    that reflected the wanted outcome) as justification to lower speed
    limits from 80 km/h to 60 km/h in some cases.
    From a GovCO letter dated 27/10/2004 in reply to my concerns about
    speed limit lowering in this area it states, with regard to
    'appropriate speed limit for a particular road':

    * pavement, shoulder and lane width
    * horizontal and vertical road alignment
    * traffic volume, activity and prevailing speeds

    And there are six more criteria but all of these conditions have been
    improved or remain unchanged on the roads in question but they remain
    20 km/h under the old long standing limit. I suspect false data
    gathering but it's hard to prove. Returning to the third 'prevailing
    speeds' is mentioned. If the pneumatic counting and speed measuring
    device is installed in a location where they have placed signs
    requiring you to travel slower due to roadwork or they are placed just
    after the roadwork then they are, to my mind, gathering false data to
    lower limits.


    I don't take sides. It's more fun to insult everyone.
  11. MC

    MC Guest

    Phenumatic tubes are still commonly used. (they're cheap and portable).
    In-road inductive-loops are much more expensive to install.

    With more that one detector (loop or tube) you can detect speed,
    direction and class of vehicle. (there are about 12 officially used
    vehicle 'types' (eg. sedan, motor bike, truck(s),
    trucks with trailers, ... )

    They cannot be 100% accurate in classifing traffic because
    inter-vehicle spacing varies with speed and road conditions,
    and there are combinations of numbers of axles and axle-spacings
    which can produce ambiguous or nonsensical classifications.
  12. Bill Gates and Paul Allen designed a micro controlled traffic analysis
    machine way back in mid-70's before Microsoft, and tried to flog it
    under their Traf-O-Data business. It might very well have been the
    first intelligent controlled traffic analysis counter. I think it used
    an 8008 micro. Scary.

    Dave :)
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