What are the two cables in some roads?

gam3r · 10 Jul 2009 at 00:14

They put a set of these weird wires outside my house a couple of months ago.

Today then installed that pointless digital speed indicator on a lamp post right outside my house. It's big and it flashes. Not impressed to say the least.

Pointless waste of money and time, everyone can read their speedo...a big flashing sign isn't going to get people to slow down.

BigglesPiP · 10 Jul 2009 at 00:34

It's the automated spike strip which is paired with an NPR camera down the road. If you're speeding, remember to lock your wheels as you go over it.

GeX · 10 Jul 2009 at 00:44

4 of these have appeared on the crossroads near my house, assuming they're monitoring traffic patterns before working out what to do about the countless amounts of accidents that happen at that junction

Stev · 10 Jul 2009 at 03:17

My next door neighbour installs these for surrey council they are purely traffic monitoring, they can also tell what kind of vehicle passed over it by wheel distance and weight (heavier it is more air it pushes) through computer interpretation, quite a neat bit of kit for "a little grey box"

iaind · 10 Jul 2009 at 07:44

Hxc said:
A guy on here who works for the government doing car-y things (I forget exactly what) said they could be used for speed, so I believe him.

I'm an ex transport minister and I design speed camera systems in my free time. Common sense says they arent accurate enough to monitor speed. Has that changed your mind?

Vanilla · 10 Jul 2009 at 08:00

So I was sitting at work (nowhere near home where I saw all the cables) yesterday and I looked out the window to my right. What do I see?

They're following me

[DOD]Asprilla · 10 Jul 2009 at 08:02

Stev said:
My next door neighbour installs these for surrey council

Does he work for Surrey Highways? If so, do you tell him every morning that he and all his colleagues are pontless sacks of ****?

You should.

Freefaller · 10 Jul 2009 at 08:42

They put them on rat runs and then see how popular they are and put lots of speed bumps.

All the side streets I used to wiggle through to get to work now have speed bumps. 3 years ago they were clear.

Freefaller · 10 Jul 2009 at 08:45

Stev said:
My next door neighbour installs these for surrey council they are purely traffic monitoring, they can also tell what kind of vehicle passed over it by wheel distance and weight (heavier it is more air it pushes) through computer interpretation, quite a neat bit of kit for "a little grey box"

It can't work. How does it know how long the vehicle is? It doesn't. If a truck goes over it at 30mph, the 2 pressure points will be quite a bit apart, if a mini goes over it at 30mph the pressure points will be closer together. How do you calibrate it without knowing or identifying each vehicle and knowing it's wheelbase?

It's purely for measure traffic volume surely!

Rich1988 · 10 Jul 2009 at 08:47

Ucof said:
Long answer: They can either check the speed of the vehicles passing over them (by which pipe pressure changes first) .

they CANNOT tell the speed

what about small heavy cars or long light cars lorries etc they are just for traffic volumes.

lolism · 10 Jul 2009 at 09:32

Freefaller said:
They put them on rat runs and then see how popular they are and put lots of speed bumps.

All the side streets I used to wiggle through to get to work now have speed bumps. 3 years ago they were clear.

Haha, same

Everywhere I have seen these cables, speed bumps have appeared.

bam0 · 10 Jul 2009 at 09:56

Rich1988 said:
they CANNOT tell the speed what about small heavy cars or long light cars lorries etc they are just for traffic volumes.

Of course they could tell the speed, if you know how far apart the cables are one set of wheels will go over both before the other set come anywhere near, speed = distance / time, it might not be super accurate but you could easily use these to determine the speed at which something drove over them.

john_s · 10 Jul 2009 at 09:58

They went through a phase round here a few years ago... where ever these sensors appeared, they were shortly followed by a gatso sprouting up, so I suspect that they may give an indication of vehicle speeds, though I don't think it be particularly accurate - I imagine they generate a fair amount of inaccurate readings. It probably gives them an idea of typical speeds though.

Dave M · 10 Jul 2009 at 10:03

If they can use the two cables to work out traffic direction they can use them to roughly estimate speed too.

I would be amazed if somebody in some council traffic office didn't ask the question.

PhillyDee · 10 Jul 2009 at 10:19

Theres a lot of them around the south side of the Tyne Tunnel at the moment. There is a major development as they are putting in a second tunnel. It looks to me like they are trying to generate an accurate picture of where all the cars are actually going before they get to the tyne tunnel, and to measure all the traffic flow for about a 2-3mile radius around the tunnel.

Freefaller · 10 Jul 2009 at 10:36

john_s said:
They went through a phase round here a few years ago... where ever these sensors appeared, they were shortly followed by a gatso sprouting up, so I suspect that they may give an indication of vehicle speeds, though I don't think it be particularly accurate - I imagine they generate a fair amount of inaccurate readings. It probably gives them an idea of typical speeds though.

What about wheelbase size? That's a hugely important factor.

If a truck goes over it at 30mph, it could equate a car doing as little as 20mph - that's a HUGE error in terms of statistics.

Sure it can measure speed, but the date would be about as useful as a diaharetic cat.

bam0 · 10 Jul 2009 at 10:39

Freefaller said:
What about wheelbase size? That's a hugely important factor.

If a truck goes over it at 30mph, it could equate a car doing as little as 20mph - that's a HUGE error in terms of statistics.

Sure it can measure speed, but the date would be about as useful as a diaharetic cat.

Why would the wheelbase matter, or the wheel size, or any other metric? To calculate the speed you would measure the time between both cables being hit by one set of wheels, so that'd give you 2 readings for a car, or 4-5 for a lorry.

Freefaller · 10 Jul 2009 at 11:22

Because the wheelbases of cars are different. They are not static. If a LWB transit does 30 over them, but a small original mini does 30, surely if they base it on the wheelbase of a medium size car, the mini well be doing over 30 and the transit will be doing under 30 no?

I'm not stating you're wrong, but surely they need to know the distance between both wheels for it to work?

markk · 10 Jul 2009 at 11:26

Front wheel goes over 1st cable - timer starts, Front wheel goes over 2nd cable - timer stops.
Rear wheel goes over 1st cable - timer starts, Rear wheel goes over 2nd cable - timer stops.

Not, front wheel goes over cable timer starts, Rear wheel goes over cable timer stops.

bam0 · 10 Jul 2009 at 11:27

Freefaller said:
Because the wheelbases of cars are different. They are not static. If a LWB transit does 30 over them, but a small original mini does 30, surely if they base it on the wheelbase of a medium size car, the mini well be doing over 30 and the transit will be doing under 30 no?

I'm not stating you're wrong, but surely they need to know the distance between both wheels for it to work?

No, that's my point they don't need to know how long the car is at all, the two cables are about a foot apart (it'll be a precise measured distance), start a timer when you receive a signal that the first cable has been hit by a wheel, stop the timer when the second cable is hit by the same wheel. You've got the distance between the two points and the time it took one set of wheels to go that distance, that gives you the speed. Imagine the car was a unicycle, it'd work fine. Imagine there are two unicyclists holding a pole that keeps one 2.5m behind the other, you'd get a reading for each of the unicyclists, that'd be how it'd work with a car.