cables on the road

Meeko said:
I fail to understand how they can be for measuring speed?!? Cars/Vans/Trucks etc all have different length wheel bases.
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There are 2 cables. It will start a timer when you cross the first, then stop when the same wheel hits the second. If you know the distance between the 2 cables you can work out the speed the vehicle is travelling at.

Drive a tank, or anything else with tracks, that'll confuse them!

PK!
 
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misterPK said:
There are 2 cables. It will start a timer when you cross the first, then stop when the same wheel hits the second. If you know the distance between the 2 cables you can work out the speed the vehicle is travelling at.

Drive a tank, or anything else with tracks, that'll confuse them!

PK!
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M'eh... I'll get my coat and book a seat on the first bus to the mentalist house. :( I was thinking it was measuring the time between the front wheels hitting the first cable and then the rear wheels hitting the second. Clealry I'm in mongo-mode today! :p
 
As stated in this thread they are there to measure congestion and teh amount of cars that go through the road.

To the guy who posted that everytime he's seen them a few months later there is a speed camera in its place....

...speed cameras are expensive. How else is the government going to know where they can outlay initial cost and be able to reap the most benefits/profit out of a spiggy bank? (Speeding Piggy Bank ;)).
 
Speed cameras are positioned based on accident rates...doesnt matter that some of these arent road accidents, but still.

The cables have nothing to do with speed and even less to do with cameras

If the cables are 1m apart they might have 10cm of flex in them (5cm either way), giving a 10% margin of error for speed. No council in the world is going to accept any speeding study with that much of a margin for error
 
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had them round here for a while, on an NSL road though. i either done my best to go over them as quickly as i could, or tried locking my brakes going over them. i missed.
 
The big thick black tubes are, as has been said, pnuematic road tubes, you only need one tube to actually count vehicles, they assume that the vast majority of vehicles over the strip are cars, so one car for every two pulses.

If you see two tubes together then 99% of the time they are measuring vehicle speed. It is not an overly accurate measurement for various reasons, but it gives the authorities a ball park number for the percentage of vehicles passing that spot that are speeding, so if teh percentage is high enough then yes speed cameras may well be installed there at a later date.

Talking of speed cameras the Truvelo (forward facing) cameras also have tubes in the road to detect the speed of the vehicle passing. However they are much thinner in diameter as they are piezoelectric (inductive loop) tubes not pnuematic, so obviously are far more accurate, as well they need to be, to measure the speed of the offending vehicles that the camera takes photos of.
 
Entai said:
Talking of speed cameras the Truvelo (forward facing) cameras also have tubes in the road to detect the speed of the vehicle passing. However they are much thinner in diameter as they are piezoelectric (inductive loop) tubes not pnuematic, so obviously are far more accurate, as well they need to be, to measure the speed of the offending vehicles that the camera takes photos of.
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I thought piezoelectric current was induced by force, ie, by striking a piezoelectric material like quartz, like in those clicky lighters. I'd always generally associated induction loops with passing metal across a magnetic loop to generate a current, like you find in car parks to open barriers or near traffic lights to change the lights for minor roads.
 
I noticed that one of the roads on my route to work had these a few days ago.
That road was a national speed limit single carriageway until a year or two back, now it's a 40mph limit with no speed cameras.

I'm fearful as to what's going to come next :(
 
Entai said:
If you see two tubes together then 99% of the time they are measuring vehicle speed. It is not an overly accurate measurement for various reasons, but it gives the authorities a ball park number for the percentage of vehicles passing that spot that are speeding, so if teh percentage is high enough then yes speed cameras may well be installed there at a later date.
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source?

because disregarding the wheelbase issue for a start, different diameter wheels will impact these strips at different 'timings' and thus will so different speeds.
 
I still dont believe they have anything to do with speed.

A good friend of mine is a civil engineer for a council and I asked him about this a while ago, he said they were always used for measuring quantity of traffic for planning roadworks etc. The 2 cables are there to measure direction of traffic when they span both sides of the road.

I may be wrong but there's no way these will be anything approaching accurate for measuring speed and I'm 99% sure speed camera locations are chosen based on accident rates. If they wanted to measure speed, why wouldnt they just use a radar device?
 
if there are 2 about 2feet apart there to check speed to see if its worth putting a speed camera up.
if its just 1 wire it counting traffic.
thoses of us that have been on the roads in the 80`s will remember that 2 were used for speed traps, thats why i always slow for them.
 
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GeX said:
source?

because disregarding the wheelbase issue for a start, different diameter wheels will impact these strips at different 'timings' and thus will so different speeds.
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http://www.jamartech.com/

Look up under the automatic traffic recorders, for TRAX Appollyon and TRAX Flex HS, both pneumatic road tube measuring systems able to record traffic volume, class, and speed from 2 or 4 tube setups.
We did loads of testing for the VCA and TRL, when Jamar wished to start importing their gear into the UK.
 
GeX said:
source?

because disregarding the wheelbase issue for a start, different diameter wheels will impact these strips at different 'timings' and thus will so different speeds.
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Not sure whether they're actually used for speed measurements or not, and has been mentioned accuracy would be dubious.

But neither wheelbase or wheelsize would make a difference *if* they were used for speed, if you measure the time (as has been mentioned) between the first and second line being triggered, and ignore the duplicate from the rear axle, you will get the speed.

Wheel size will barely affect the result for one trigger, and will affect the second by the same amount...
 
SKILL said:
Not sure whether they're actually used for speed measurements or not, and has been mentioned accuracy would be dubious.

But neither wheelbase or wheelsize would make a difference *if* they were used for speed, if you measure the time (as has been mentioned) between the first and second line being triggered, and ignore the duplicate from the rear axle, you will get the speed.

Wheel size will barely affect the result for one trigger, and will affect the second by the same amount...
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Exactlly, and if you set the criteria for "speeding" as 10 to 15 mph over the posted limit say, then you will get a reasonably accurate percentage of vehicles that are speeding at the point they cross the tubes.
Exact accuracy with regard to individual speed of individual vehicles is not needed, it is only a measurement of a rough idea so that they can see if the general trend is to speed at that point or not.
 
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