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rubber hose/sensor lines across road?

Discussion in 'The Pub' started by nibor, Jul 28, 2009.

  1. the two rubber lines/sensor cables you often see nailed perpendicularly across a road, connecting to a data box chained up to something, what are these for?

    vehicle mass detection, vehicle type, vehicle frequency counters, speed detection, what? obviously they simply collect raw data, none of it can be identified to a specific motorist.

    at the moment i tend to slow down for them, simply in case they do detect speed, i dont need any more governments deciding more speed limit reductions or chicanes or speed bumps are required.
  2. They don't detect speed. To much variance in the wheel base etc to do that.

    From memory they are traffic counters
  3. But why would there be two lines run across the road, a counter only needs one line, but the presence of two lines at a fixed distance means they can measure speed as the front (OR back) wheel crosses and the time is measured.
  4. exactly, and they always seem spaced at the same width.
  5. And every vehicle has the same wheelbase?

    I'm going to hazard a guess. It could be so that they can detect when a multiple axle vehicle has run over them (and vehicles with trailers).
  6. Wheelbase has nothing to do with it. It measures the time taken from tripping one line to the next - this can indicate speed. I have spoken to council folk about these and yes, they record speed, there was one out the front of my house for a while. They said they may/may not report it to the police but it's there more so for road use statistics and maintenance schedules.
  7. Oh yeah - Doh! dunno what I was thinking there... mind was on something else.
  8. Yes, they do detect speed !

    Working out at Cadia Mine years ago, the mine safety committee decided to put these cables across on Cadia Rd (Orange, NSW). This was done in secrecy to enforce that vehicle safety also extends to the road outside of the mine site.

    The results were posted up on the notice boards with great surprise.

    One result showed a multi-axle truck tripping the wires at 150+ km/h ! :eek: It showed the date, time and speed. The results also showed that the majority of the vehicles travelling from the mine (ie going home) were speeding, while the vehicles travelling to the mine travelled at a less speed.

    No doubt the results made everyone rethink their driving attitudes.
  9. sweet. thanks for the info guys!
    i shall continue to distort the statistics and slow down for these mofo's :grin:
  10. Some are used by council to detect the number of vehicles using a street. The two tubes allow them to work out which direction the vehicles are traveling. This is then matched to the time the vehicles are using the street. This allows the council to gain supportive evidence for residents complaints and allows them to work out measures to deal with traffic whether it be by signs or engineering measures such as speed humps, chicanes, etc.

    Some do measure speed. I am not sure of how many of the council ones do but the police ones are called amphometers.

    This is a Tasmanian legislative reference to them (As it was one of the first to appear after my google search :) ) : http://www.austlii.edu.au/au/legis/tas/consol_reg/vatddr2002452/s7.html

    As mentioned above, the tubes are set at a set distance apart and when the first set of wheels pass over the first tube the time to the second one is measured thereby calculating the speed. Old technology.
  11. Don't slow down too much or your data will be outliers and will be filtered out when the the results are interpreted.

    Likewise don't bother flying over it at 150, the person who looks at the data will just have a good laugh and it won't mean anything after the outliers are again removed from the data.

    I've had these on the street behind my house where i don't want street calming devices put in. I purposely always drove past them at 10km/h below the limit such that my results will hopefully contribute to a end result where traffic calming is deemed not necessary.

    Essentially, so i can hoon through my backstreets at 80.
  12. Handbrake lock-up in a cage crossing them usually fixes them. :LOL:
  13. Maths time (yep, no work);

    Assume the equipment has to have the tapes / tubes 30cm apart to detect speed correctly.

    .: d = 0.3m

    Assume device only records speed using front wheels only. Uses remaining wheels to determine vehicle type / traffic flows.

    100km/h / 3.6 = 27.8 m/s

    d / s = t;
    .: 0.3 / 27.8 = 0.011s

    So when the device records a time gap of 0.011s, it records the vehicle doing 100km/h.

    However, the operator is from VicRoads and can't do anything right and doesn't place the tubes EXACTLY 0.3m apart, he places them a GREATER distance apart, X

    (d + X) * 3.6 / t = s

    d = 0.3m
    X = 0.1m (operator placed them 0.4m apart)
    t = 0.011s

    (0.3 + 0.1) * 3.6 / 0.011 = 131 km/h !!

    Likewise, the operator places the tubes to close;

    d = 0.3m
    X = -0.1m
    t = 0.011s

    (0.3 + -0.1) * 3.6 / 0.011 = 65.5km/h !!

    Let Y equal the variation in speed.


    (0.3 + X) * 3.6 / 0.011 = (100 + Y)


    327.27 * X - 1.82 = Y

    So for 5cm out the tubes are placed, there will be an approximate error of 15km/h read for that machine, assuming they are required to be placed at 30cm.

    Or, universal formula;

    (3.6 * X) / t + (3.6 * d) / t - S = Y

    d = distance in meters machine requires tubes to be placed apart.
    t = expected time taken for vehicle traveling at S speed to cross both tubes.
    S = vehicle speed
    X = variation in distance of tubes from d
    Y = variation in speed detected by machine

    I've just realised at the end of all that, there was no real point to it all.........

    *climbs back in box*
  14. Woot sexy maths.

    If you have ever looked at cars going over the cables you will notice that the cables to move back and forth a bit each time.
    I think that would throw out even more errors esp on multi land roads.
  15. Ah you young'uns. Once upon a time this was the ONLY reasonably accurate way the cops used to detect your speed. They would sit by the side of the road watching the display on one of these things and then chase down any villains who didn't spot the lines in time.

    Now only used for stats, but if you see someone brake hard before hitting one you can be fairly sure it is an old codger like me who still reacts instinctively when we see 'em. :wink:
  16. I wonder what would happen if we pushed a line of 50 trollies over these things several times :cheeky:
  17. level crossing lights?
  18. It wont significantly affect the purpose of collecting the data.
  19. Yeh, but whats funny is when you see the local kids sitting in the gutter with rocks banging away on them. Imagine the stats collector........."Holy crap that was going faster than a bloody concord, round this f#%ing corner! :grin: :grin:
  20. :rofl:

    They are simply AADT counters!

    They are one of the most important tools used in my line of work.
    They can be used to measure speed, however it is inamissable, due to the primative technique used to trigger the counter.

    It is essentially hollow rubber hose, and every time an axle crosses it, it compresses, and forces air in to the collection box, which then ticks the meter over. Nothing more, nothing less.

    You can bett your house, that if you see one of these about, very soon you will have your road either resurfaced, or shuffled back to the bottom of the pile!

    Trust me, I know stuff.