What are these cables running across the road?

r3nu4l

Joyfully someone know what I'm talking about here...

Occasionally, on a stretch of road I see two cables about half a metre apart, stretching across the road, then maybe a kilometre away there will be two similar cables.

I assume these are used for traffic monitoring, perhaps recording volume and time to travel between two distances.

However I'm aware that assumptions are dangerous

So can anyone enlighten me as to what these cables are for and when they are used.

paulbok

r3nu4l wrote: »

Joyfully someone know what I'm talking about here...

Occasionally, on a stretch of road I see two cables about half a metre apart, stretching across the road, then maybe a kilometre away there will be two similar cables.

I assume these are used for traffic monitoring, perhaps recording volume and time to travel between two distances.

However I'm aware that assumptions are dangerous

So can anyone enlighten me as to what these cables are for and when they are used.

They are fir counting traffic. Every time a vehicle passes over then it generates a current and feeds back to a counter at the side if the road.

Avatar MIA

paulbok wrote: »

They are fir counting traffic. Every time a vehicle passes over then it generates a current and feeds back to a counter at the side if the road.

That was my understanding as well, although I assumed the second "wire" was to calculate speed.

Sam Russell

I think they are air tubes not cables. The air pressure goes to a switch which counts the traffic. Cables would be damaged by the traffic, tubes are cheap to replace - the clever bit is in the box at the side of the road.

[At least that was the way it used to be done. If cables are used, they are buried in the road.]

paulbok

Sam Russell wrote: »

I think they are air tubes not cables. The air pressure goes to a switch which counts the traffic. Cables would be damaged by the traffic, tubes are cheap to replace - the clever bit is in the box at the side of the road.

[At least that was the way it used to be done. If cables are used, they are buried in the road.]

You could well be right on the air tubes, I always assumed they were an induction cable loop.

Alun

paulbok wrote: »

You could well be right on the air tubes, I always assumed they were an induction cable loop.

They are air tubes. They aren't connected together at the other end to the measuring equipment so wouldn't form a loop anyway.

tphase

Avatar MIA wrote: »

That was my understanding as well, although I assumed the second "wire" was to calculate speed.

could also be used to determine direction

annfield1978

ATC Automatic Traffic Count

L1011

Software to analyse the results from these was what started Bill Gates off in the software industry oddly:

https://en.wikipedia.org/wiki/Traf-O-Data

vince

Seen those pipes around alot. Is it the same sort of thing near traffic lights you see a rectangle of mastic in the tarmac looks like burried cables.

vince

vince wrote: »

Seen those pipes around alot. Is it the same sort of thing near traffic lights you see a rectangle of mastic in the tarmac looks like burried cables.

No, that's the sensor for the traffic lights, to let them know there's a car there waiting.

Godge

Deleted User wrote: »

No, that's the sensor for the traffic lights, to let them know there's a car there waiting.

It is amazing the number of drivers who don't know about those sensors. Getting stuck behind one is a nightmare.

L1011

Godge wrote: »

It is amazing the number of drivers who don't know about those sensors. Getting stuck behind one is a nightmare.

I suspect some taxi drivers in quiet periods deliberately under or overshoot them to elongate the journey. Take note of what cars are missing them!

L1011

L1011 wrote: »

I suspect some taxi drivers in quiet periods deliberately under or overshoot them to elongate the journey. Take note of what cars are missing them!

I tend to stop on the one second from the lights, speeds them up a bit (sometimes).
Most lights simply appear to use a dumb timer, even when they have the loops. :mad:

guylikeme

One could get their road prioritised by falsifying the data by simply cycling over and over it like a madman so that the gov thinks that more traffic uses the route and open the chequebook

guylikeme

guylikeme wrote: »

One could get their road prioritised by falsifying the data by simply cycling over and over it like a madman so that the gov thinks that more traffic uses the route and open the chequebook

I suspect that the sensors are smarter than that and look at the volume of air moved by the tyres of the vehicles to determine type..
Bicycle tyres would register a small puff of air, HGV big puff!

Hook up a compressor and a programmable pneumatic actuator then you could simulate the traffic flow of a truck racing grand prix!

Sam Russell

Deleted User wrote: »

I tend to stop on the one second from the lights, speeds them up a bit (sometimes).
Most lights simply appear to use a dumb timer, even when they have the loops. :mad:

Some lights wait until no traffic hits the detector for a predetermined time - like 30 seconds of no traffic even if there is only one vehicle every 25 seconds. There is usually a secondary timer like 5 mins that kicks in if there is a constant stream of traffic. The light then changes and changes back after 10 seconds because your road is not important enough.

As you say - dumb.

Red Fred

Avatar MIA wrote: »

That was my understanding as well, although I assumed the second "wire" was to calculate speed.

qqqq

Sam Russell

Avatar MIA wrote: »

That was my understanding as well, although I assumed the second "wire" was to calculate speed.

Speed and direction, but not always speed - the box needs to be a bit cleverer for that.

stoneill

The traffic count sensors use a pair of tubes. As the car passes over it generates a pressure differential that is monitored. The second tube will calculate direction by the time different in tube a and tube b.

The buried sensors are a simple induction coil. A vehicle will alter the magnetic field of the coil that is registered by the circuit.
A bicycle is not big enough to alter the magnetic field.