Cables across the road?

[Golden Boy]

Sure to have been mentioned before, but what are the pair of cables that go across the road that turn up from time to time?
They abviously measure something but don't seem to be attached to anything.

[streaky]

They are pneumatic tubes. Singles record traffic volumes by ToD, doubles record speed by ToD - Streaky

[Nickccc]

www.pistonheads.com/gassing/topic.asp?f=23&h=&t=172526
all here

[Boosted LS1]

Just slow when you see 3 cables! There will be a camera on a tripod nearby and a couple of tts around the corner minding their own business! Tossers.

[puggit]

They are being used to see if a Scamera would earn enough revenue

[towman]

streaky said:

doubles record speed by ToD - Streaky

So how about when I`m in a 3 axle truck? - a slow unicyclist being chased by a very fast car?

[Pigeon]

No - a car being followed by a succession of incredibly long vehicles sat right up each other's arses.

[streaky]

towman said:

streaky said: doubles record speed by ToD - Streaky So how about when I`m in a 3 axle truck? - a slow unicyclist being chased by a very fast car?

It doesn't matter. The doubles record the time of each compression. Simple maths gives the speed (and direction if the tubes are right across the road) at which the axle (and therefore the vehicle) was travelling. On analysis the speeds are broadly categorised (20-30, 30-35, 35-40, or similar). No great accuracy is needed.

An algorithm is used to level out the count with the single (traffic volume) counters by allowing for vehicles with more than two axles. This can be done with the double tubes, but is less necessary.

Forgot to say earlier that tha DS2 speed camera system uses three strips (laid on top or set into the road surface). The strips are more widely separated (the double speed counters are some 18" apart) and the system is linked by wire to a permanent short grey (usually) post and then to either a van-housed or tripod-mounted camera - but only when actually in use.

Streaky

['King Deadly]

The last set of those cables I saw was about a month ago. Two weeks later, up popped a brand new Gatso. There's no calibration marks on the road yet, though. (Alexandra Road, Moss Side, Manchester, for those that know it.)

[puggit]

What did I say?!

[boredpilot]

I too have wondered how the 2 cables can do anything other than determine direction and an approximate volume of traffic.

My midget has a different axle spacing to most modern cars so how would they know the speed of a vehical if axle distances are all different? I know they say they can have a list of many different axle spacing but how does it know what the vehichal is. (It cannot be by weight since I could have me + realy big pax and about 150kg worth of sand in the boot of the midget. That alone could put the weight of the car from around 690kg to 900+ kg.

EDIT TO SAY wow PH having the gremlins today, It didnt show me the last 5 posts when I posted this.

>> Edited by boredpilot on Sunday 8th May 11:39

[Eliminator]

Unless your axels are less then 18 inches apart, your front wheel hits cable 1 then cable 2, then there is a short gap before your rear axel follows. Speed is taken from the difference in time between one axel hitting both tubes. Therefore does not matter how your axels are spaced.