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  4 1 They technically count axles and how long it takes the axles to pass between the two tubes, from which you can infer speed. There's a lot of uncertainty-- i.e. you don't know how many axles a car has (obviously an 18 wheeler will count as several cars) and since you don't know the wheel base (distance between the axles) on every car, you can't precisely measure speed. And yes a bicycle or punk kids jumping on it will set it off, although unless they time their jumps just right the'll probably get thrown out as outliers. But they generate a lot of data so you can make educated guesses, particularly as to the level of car vs. truck traffic, especially if it's a road that's been measured the old fashioned way (i.e. guy with a clipboard). And it really is just to give a rough idea of the relative traffic volume and speed in an area-- it's not like even having a 100% precise measuring device would provide data that was much more useful, given how chaotic traffic is as a system. Jack answered in Cars, Bikes & Transit about 1 year ago | Report Comment on this answer Enter your comment or ask a new question preview THIS IS A PREVIEW: Click "Post" to submit it or "Edit" to make changes. edit Please wait… This could take a minute if the tubes are clogged.

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  1 2 they merely count cars going over them and are gathering mushy data at best: 100 pound guys stomping on them can activate a click. So, yes, bikes can click them too, especially if you wheelie and land the center of the tire on it. There's a delay built in so the rear axle doesn't count a second time, but I'd presume slow-moving cars would count on them twice. Rev.Enant answered in Cars, Bikes & Transit about 1 year ago | Report 4 comments by BasementDweller3, Urgutha Forka, and Rev.Enant… 0 0 Why are there two cables if they are counting one car? I always thought they had 2 for speed. BasementDweller3 commented about 1 year ago | Report 0 0 Those things are far too crude to calculate speed. The accuracy would blow. I think Rev. Smith is right, they're only ticking up raw numbers of cars going over them. Urgutha Forka commented about 1 year ago | Report 0 0 Well, to wit, there's only a 5 or 6 digit click-counter readout... like a odometer, but cruder. i.e. it's a mechanical, not digital device. And I'm presuming the second tube is actually for the other lane... one long (far lane) and one short (near lane), since I've seen that before. Rev.Enant commented about 1 year ago | Report 0 0 I have heard that they install two hoses so that if one springs a leak, they have a second one counting. I've also heard that occassional variances mean some of the impacts on the hose don't count, and others trip twice. As a result, you install two hoses, two counters and average the two readings together. Or so I've heard. And yes, they calculate a couple of pesky meddling kids playing in traffic too... "Cagey" commented about 1 year ago | Report Enter your comment or ask a new question preview THIS IS A PREVIEW: Click "Post" to submit it or "Edit" to make changes. edit Please wait… This could take a minute if the tubes are clogged.

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