cables on the road

wijcc · 20 May 2009 at 15:06

Does anyone know what the two black cables they lay on the road is for.. i have started noticing that there are more and more of these two black cables/wires that they are laying on the roads in London.. what are they used for??
THanks in advance guys

iaind · 20 May 2009 at 15:07

Counting traffic...

Ringiho · 20 May 2009 at 15:09

I thought they checked speed, for when 'they' are considering putting in speed cameras.

paradigm · 20 May 2009 at 15:09

I thought they were laid down so you could see if you can snap them by locking up over them

Fr0dders · 20 May 2009 at 15:09

as above, they are used for measuring congestion

eveytime you drive over them it records a break in the pressure.

Helps to give road planners an idea of traffic flow as it logs the date and time of the car passing as well. you'll usually see the little grey box they're connected to that stores the data.

iaind · 20 May 2009 at 15:13

Exactly, they are quite often used when they are considering doing some sort of roadworks so they can plan diversions etc.

There are 2 so they know the direction of the traffic, nothing to do with speed

-Ad- · 20 May 2009 at 15:14

Claymore mines.

wijcc · 20 May 2009 at 15:23

cool thanks guys

Justintime · 20 May 2009 at 15:26

Heard if they're 3 then speed is being checked?

Bill101 · 20 May 2009 at 15:42

Justintime said:
Heard if they're 3 then speed is being checked?

If every vehicle on the road had the same wheelbase then they might be able to approximate the speed

paradigm · 20 May 2009 at 15:46

Bill101 said:
If every vehicle on the road had the same wheelbase then they might be able to approximate the speed

They don't need to know the wheelbase, the cables are that close together that the front axle will have passed all three cables before the rear axle touches the first.

You'd just have to discard the duplicate readings (from multiple axles).

InvaderGIR · 20 May 2009 at 15:50

iaind said:
There are 2 so they know the direction of the traffic, nothing to do with speed

What about when they are on a dual carriageway then? I've driven over some that were alongside laybys, and appeared to have trailing cables in the layby.

DanTheMan · 20 May 2009 at 15:50

90% of places I've seen them around here, a speed camera has been placed in the same spot a few months later.

Ringo · 20 May 2009 at 15:51

I heard if there are 4 they are checking the weight of the driver

Meeko · 20 May 2009 at 15:58

If there are 5 of them, its for pregnancy tests (female drivers only obviously)

Dogbreath · 20 May 2009 at 16:02

They are for doing a traffic survey, either volume or speed to see whether traffic calming measures or speed cameras should be introduced.

Gaygle · 20 May 2009 at 16:03

If there are 6, it's definately to measure blood pressure of the driver.

Steeps · 20 May 2009 at 16:07

Our area had 2 strips a while ago, then placed those lightup speed signs a few weeks later on some of the patches. According to a council member the strips were measuring how many drivers were over the limit and those roads with excessive amounts of speeding traffic got the new flashy signs.

Meeko · 20 May 2009 at 16:13

I fail to understand how they can be for measuring speed?!? Cars/Vans/Trucks etc all have different length wheel bases.

alle · 20 May 2009 at 16:17

...What has wheelbase got to do with it?