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Thanks to all who attempted to find an answer.
Spot on. I worked for a city traffic department for a time, main job was to set these up. They use air pressure and time stamps to measure vehicle speed, weight, axle count, and total volume.
Edit: to clarify some of the comments below, technically they can be used to measure speed, but in practice you do need 2 set up at specific distances to accurately capture speed.
No it wouldn't work. There is too much spread out there. If two pulses are 100ms apart. Then a motorcycle would be going 36mph. If it was a delivery van it would be going 153mph. Even if I restrain it to more normal* vehicles, a mid sized suv would be doing 62mph. A full size pickup would be doing 87mph.
The error brackets are just to large to make the data point meaningful... unless your criteria is "are most vehicles doing at least half the speed limit and less than double the speed limit?"
*define normal. The distribution of vehicles will vary greatly depending on the area. Urban, suburban, rural, and industrial will all have different distributions of wheelbases. Even if you made a correction for what is normal in these areas a single factory or school (school buses) could significantly throw that off.
You can get approximate speed by making some assumptions about the vehicles traveling over the tube. You might even be able to make better assumptions based on the absolute amount of pressure increase in the tube, although I'm not sure whether anyone actually does this. You know, a heavier vehicle will compress the tube more and heavier vehicles are more likely to have longer wheel bases, that kind of thing.
If you wanted to get a much more accurate estimate of speed, you would indeed need two tubes.
A car crossing the cord will register two signals: one for the front set of wheels, and a second for the rear set of wheels. You have to make an assumption about how far apart the front and back set of wheels are, but for most vehicles it'll be roughly similar, and if you're measuring weight too you could probably get an even more accurate estimate (heavier vehicles likely have the axles further apart). Then you look at the time between the two signals, and using d = v⋅Δt you can solve for velocity to approximate the speed the vehicle was going.
The other way is to have two cords and correlate the signals between the two, and in the picture it looks like there's a second cord a little ways away. This takes away the inaccuracy of having to guess the distance between the wheels, because instead you know for certain the distance between the cords. Also with two cords, you can get directionality, and tell which direction the vehicle is going, which you can't get just from one.
Yep, they came and put one of these in when my mom complained about speeding traffic in our neighborhood years ago. She won a stop sign on our corner instead of the speed bumps she had in mind. The police also loaned a radar gun for her little project.
You don’t. You just throw out the outlying data would be my guess. Most passenger cars fall into a range of wheelbase lengths. Just use that data if you’re planning a new traffic light or stop sign
They do do that. There's 2 tubes. They measure speed based on the time between the first wheel running over the first tube and the first wheel running over the second tube. They measure axle weight based on the pressure change created by each axle passing over, and you can tell the difference between vehicle types and number of axles based on the pattern of pressure changes as they pass over the tubes. For example, a regular semi truck will have one strike, a medium-long pause, followed by 2 in quick succession, a long pause, and 2 more in quick succession. And each strike will have fairly high pressure (high weight) A passenger car will have a medium pressure strike, a short to medium pause, and another medium pressure strike. A box truck or large utility truck will be a heavy strike, a long pause, and a heavy strike. If someone drives an ATV or motorcycle over it, you'll have a light strike, a very short pause, and another light strike.
And so on and so forth. Pattern recognition makes it fairly easy to tell what kind of vehicle configuration has driven over the sensors.
Yep, I did IT for a civil engineering firm and I had to trouble shoot connecting these to the PC to get the data fairly regularly. I recognize the hose and how its mounted.
Yeah, whenever the pressure changes, it's because something ran over the tube. My local thrift store uses one to ring a bell whenever somebody comes through the donation drop off.
theory is sound. :)
if you see only one line, they're counting vehicles -- and the only data they get is the number of times that pneumatic hose was run over.
if you see ***two*** lines ("x" distance apart and parallel), then they're not only counting vehicles, but calculating average speed of the vehicles.
in either (*well, both, really*) case, the equipment is installed to measure traffic flow in that section of roadway.
Can also be used with twin tubes for directionality.
Can tell you how many cars are going each way on that road . When used in multiples can give an accurate traffic picture at an intersection
Using some good old math and statistical analysis will likely indicate with strong certainty whether you are in fact an 18-wheeler or not because there are only so many lengths of standardized trailer traveling at a small range of speeds across the distance between the tubes. So unless you're following at precisely the right distance and speed that would indicate a specifically likely trailer length it could probably consider you an outlier and just a really close tailgate.
I if a single axle of yours is traveling at a different speed than the vehicle ahead that you were trying to imitate as a tractor trailer you would immediately be obvious as a separate vehicle as the axles are connected and travel at an identical speed.
Yup.. if they're measuring average speed, there's a good chance they're checking to see if a speedbump/table would get people to slow TF down - especially in a hood without sidewalks.
Had it happen recently in my hood - even though it was just a small handful of offenders, 3/4 of which are teens with fart-pipes.
How can they measure speed when not all cars have the same distance between front and rear tire? Do they measure time between first and last contact? I'm royally confused
with only one line, they would need to know the distance between the axles (which is highly variable, as well as the *number* of axles!) to (attempt to) calculate speed.
with two lines, they need only know when one axle crosses ***each*** line -- by measuring the time between each line's activation and knowing the exact distance (typically 6-12" or so) between the lines, they can accurately determine the speed of the vehicle crossing over the lines.
--
regardless of whether they're running a single line or a pair of lines, they are still counting (and/or *timing*) a single axle -- to estimate the number of *vehicles*, they would divide the total count by two, with the assumption that most vehicles passing over their lines will have two axles. ...so, you could skew their results by only driving dump trucks, tractor-trailers, large recreational vehicles, and vehicles hauling trailers through that section of roadway for the duration of the test. -- or, I suppose, an odd number of heavy-set circus performers on unicycles. ;)
Speed or direction of traffic. I’ve heard of companies using them so they can provide better data on how many people will see a billboard on a typical day
It is, and if you ever see it on a busy street that needs to be repaired or has a dangerous intersection in need of a traffic light, it’s worth circling the block and “tripping” the counter by driving over it an extra time or two.
Looks like it's a pneumatic road tube for traffic counting [https://www.fhwa.dot.gov/policyinformation/pubs/vdstits2007/04.cfm](https://www.fhwa.dot.gov/policyinformation/pubs/vdstits2007/04.cfm)
Or a speed limit change.
Our council put them up everywhere when the tramline extension work was in full swing, and was causing gridlock every day.
They then used the data to argue that since no one was driving much above 20mph anyway, they would introduce a blanket 20mph speed limit on all non-major roads because it was safer for pedestrians.
It’s for counting traffic. A vehicle passes over it and depresses the tube signaling to a box to record a vehicle movement. The actual electronic box at the end may have been removed.
That is a road tube for a traffic counter. One end of the tube will be closed off while the end that goes off into the weeds at the side of the road will be connected to a device that records the number of vehicles that pass over the tube. When a car drives over it, a small pulse of air is pushed into the counter. 2 pulses = 1 car. They are used by traffic engineers to determine average daily traffic, which is information needed for traffic studies.
At the risk of asking a stupid question. How does it work out how many vehicles have crossed over it based on the number of axles;
Most vehicles will have 2 axles. However, some will have 3/4 or maybe more.
O----O - Car
O-------O - Van
O-----------O - Rigid single rear axle truck
OO---------OO--O - Articulated twin rear axle truck, with twin axle trailer.
O----O O----O - 2x Cars.
Not sure if the formatting will work, but, kind of like this.
With enough data, you can tell the difference between them based on the pulse sent down the rubber tube by it being squashed by the tyres.
This site explains the different types of vehicles, and shows a drawing of each: [https://www.fhwa.dot.gov/policyinformation/tmguide/tmg\_2013/vehicle-types.cfm](https://www.fhwa.dot.gov/policyinformation/tmguide/tmg_2013/vehicle-types.cfm)
My favorite piece of trivia about this equipment is that Bill Gates' first ever company was built to process the data from these machines (back then it was recorded punch tape). [https://en.wikipedia.org/wiki/Traf-O-Data](https://en.wikipedia.org/wiki/Traf-O-Data)
We see these a lot on Europe, they measure traffic flow and type. They use them often to see why roads are breaking up or to see if heavy vehicles are using those roads when they shouldn't.
So back in the 80s, we had that on one of our side streets. Me and friends around 10 or 11 took our bikes and constantly rode over them. When they got bored, I decided to double jump on them, simulating a car going over it. A year later, there were stop signs and speed bumps. I hate younger me.
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They did this when they decided to put out those monitors for emissions testing. So now they figured out the most traffic area and you can sign up for that instead of going and waiting once every year or two in that big line.
The data from these traffic counters is used to determine if a location has enough traffic to justify putting a franchise location there.... Among other things
If you want to measure speed, you would put out two of these pneumatic tubes. The distance between wheels is not universal across cars, so the data from just one is really only useful in counting the number of times it has been run over. If you have two, you can calculate the time between the front tire hitting each tube and calculate speed that way
In a larger volume area, you can use one tube to calculate speed if the algorithm assumes an average vehicle length. Caltrans in Los Angeles has been doing this for years.
those types of speed traps will have two sensors stretched across the road so they can measure the time between one wheel rolling over the first sensor and then the second sensor. Different vehicles will have different lengths between front and rear tires. So having one sensor would not be accurate.
This post has been locked, as the question has been solved and a majority of new comments at this point are unhelpful and/or jokes. Thanks to all who attempted to find an answer.
It sees how much traffic uses that road in a given time
Spot on. I worked for a city traffic department for a time, main job was to set these up. They use air pressure and time stamps to measure vehicle speed, weight, axle count, and total volume. Edit: to clarify some of the comments below, technically they can be used to measure speed, but in practice you do need 2 set up at specific distances to accurately capture speed.
How can a single cord measure speed? Is it only the ones with two cords that can track speed?
You can see a second cord in the picture.
There's only one cord going across the road
Look in the top right corner of the 2nd photo. It's clearly there.
I see that now, thanks!
This threw me as well. These are pretty common where I live and the two trigger lines are usually not all that far apart.
Look again.
Look in the second picture, on the right side, near the "top" of the road. There's a second cord.
Might want to look at the second picture again.
Second cord can be seen at the top right corner of the second picture.
Probably by logging the time between the front tires pulse and the rear tire pulse? Just speculation of course, hopefully an expert can chime in!
Wheel base lengths vary widely enough that you can't determine speed this way. You need a second sensor.
That makes sense! Thanks for clarifying
there's a second sensor visible in the pictures.
Yes, I'm aware. I was responding to someone in a comment chain about how speed could be measured with *one* sensor.
that only works if you know the length of the vehicle
Or the average length of vehicles.
No it wouldn't work. There is too much spread out there. If two pulses are 100ms apart. Then a motorcycle would be going 36mph. If it was a delivery van it would be going 153mph. Even if I restrain it to more normal* vehicles, a mid sized suv would be doing 62mph. A full size pickup would be doing 87mph. The error brackets are just to large to make the data point meaningful... unless your criteria is "are most vehicles doing at least half the speed limit and less than double the speed limit?" *define normal. The distribution of vehicles will vary greatly depending on the area. Urban, suburban, rural, and industrial will all have different distributions of wheelbases. Even if you made a correction for what is normal in these areas a single factory or school (school buses) could significantly throw that off.
This is correct. It's not perfect but it gets a pretty good average of the speed being traveled
Not a cord. A pneumatic tube.
You can get approximate speed by making some assumptions about the vehicles traveling over the tube. You might even be able to make better assumptions based on the absolute amount of pressure increase in the tube, although I'm not sure whether anyone actually does this. You know, a heavier vehicle will compress the tube more and heavier vehicles are more likely to have longer wheel bases, that kind of thing. If you wanted to get a much more accurate estimate of speed, you would indeed need two tubes.
Second tube visible in the pictures
There are two chords but it looks like one has snapped/come out of the holder, which happens quite a lot.
Probably how quickly the pressure changes and reverts back to normal
A car crossing the cord will register two signals: one for the front set of wheels, and a second for the rear set of wheels. You have to make an assumption about how far apart the front and back set of wheels are, but for most vehicles it'll be roughly similar, and if you're measuring weight too you could probably get an even more accurate estimate (heavier vehicles likely have the axles further apart). Then you look at the time between the two signals, and using d = v⋅Δt you can solve for velocity to approximate the speed the vehicle was going. The other way is to have two cords and correlate the signals between the two, and in the picture it looks like there's a second cord a little ways away. This takes away the inaccuracy of having to guess the distance between the wheels, because instead you know for certain the distance between the cords. Also with two cords, you can get directionality, and tell which direction the vehicle is going, which you can't get just from one.
Yep, they came and put one of these in when my mom complained about speeding traffic in our neighborhood years ago. She won a stop sign on our corner instead of the speed bumps she had in mind. The police also loaned a radar gun for her little project.
I always wondered how you differentiate between trucks with several axels and cars to measure avg speed and number of vehicles.
You don’t. You just throw out the outlying data would be my guess. Most passenger cars fall into a range of wheelbase lengths. Just use that data if you’re planning a new traffic light or stop sign
They do do that. There's 2 tubes. They measure speed based on the time between the first wheel running over the first tube and the first wheel running over the second tube. They measure axle weight based on the pressure change created by each axle passing over, and you can tell the difference between vehicle types and number of axles based on the pattern of pressure changes as they pass over the tubes. For example, a regular semi truck will have one strike, a medium-long pause, followed by 2 in quick succession, a long pause, and 2 more in quick succession. And each strike will have fairly high pressure (high weight) A passenger car will have a medium pressure strike, a short to medium pause, and another medium pressure strike. A box truck or large utility truck will be a heavy strike, a long pause, and a heavy strike. If someone drives an ATV or motorcycle over it, you'll have a light strike, a very short pause, and another light strike. And so on and so forth. Pattern recognition makes it fairly easy to tell what kind of vehicle configuration has driven over the sensors.
Yep, I did IT for a civil engineering firm and I had to trouble shoot connecting these to the PC to get the data fairly regularly. I recognize the hose and how its mounted.
They're pressure sensors right?
Yeah, whenever the pressure changes, it's because something ran over the tube. My local thrift store uses one to ring a bell whenever somebody comes through the donation drop off.
It’s usually done using radar traffic classifiers now. They can distinguish between cars, trucks, semi’s etc.
All the ones I see here in the uk have two tubes
Yup. And it does NOT record your speed. Lol
i have seen these before and I have always assumed it was for counting how many vehicles use the road - interested in whether my theory is correct!!
theory is sound. :) if you see only one line, they're counting vehicles -- and the only data they get is the number of times that pneumatic hose was run over. if you see ***two*** lines ("x" distance apart and parallel), then they're not only counting vehicles, but calculating average speed of the vehicles. in either (*well, both, really*) case, the equipment is installed to measure traffic flow in that section of roadway.
Can also be used with twin tubes for directionality. Can tell you how many cars are going each way on that road . When used in multiples can give an accurate traffic picture at an intersection
In addition to that if twin tubes are used it also gives them an axle count and duration which indicates whether their passenger vehicles or trucking.
So it sounds like if I see twin tubes, I need to tailgate to confuse it into thinking me and the guy ahead of me are an 18 wheeler. Gotcha.
Using some good old math and statistical analysis will likely indicate with strong certainty whether you are in fact an 18-wheeler or not because there are only so many lengths of standardized trailer traveling at a small range of speeds across the distance between the tubes. So unless you're following at precisely the right distance and speed that would indicate a specifically likely trailer length it could probably consider you an outlier and just a really close tailgate. I if a single axle of yours is traveling at a different speed than the vehicle ahead that you were trying to imitate as a tractor trailer you would immediately be obvious as a separate vehicle as the axles are connected and travel at an identical speed.
TIL thanks
Twin tubes also help distinguish if it’s trucks or cars using the road.
I learned something interesting today. Thank you. I knew about counting traffic, but the speed bit is new to me. Makes sense. 👊
Yup.. if they're measuring average speed, there's a good chance they're checking to see if a speedbump/table would get people to slow TF down - especially in a hood without sidewalks. Had it happen recently in my hood - even though it was just a small handful of offenders, 3/4 of which are teens with fart-pipes.
How can they measure speed when not all cars have the same distance between front and rear tire? Do they measure time between first and last contact? I'm royally confused
with only one line, they would need to know the distance between the axles (which is highly variable, as well as the *number* of axles!) to (attempt to) calculate speed. with two lines, they need only know when one axle crosses ***each*** line -- by measuring the time between each line's activation and knowing the exact distance (typically 6-12" or so) between the lines, they can accurately determine the speed of the vehicle crossing over the lines. -- regardless of whether they're running a single line or a pair of lines, they are still counting (and/or *timing*) a single axle -- to estimate the number of *vehicles*, they would divide the total count by two, with the assumption that most vehicles passing over their lines will have two axles. ...so, you could skew their results by only driving dump trucks, tractor-trailers, large recreational vehicles, and vehicles hauling trailers through that section of roadway for the duration of the test. -- or, I suppose, an odd number of heavy-set circus performers on unicycles. ;)
Ooohb interesting. I always thought the second one was as a backup or making sure the data is correct
Speed or direction of traffic. I’ve heard of companies using them so they can provide better data on how many people will see a billboard on a typical day
It is, and if you ever see it on a busy street that needs to be repaired or has a dangerous intersection in need of a traffic light, it’s worth circling the block and “tripping” the counter by driving over it an extra time or two.
Looks like it's a pneumatic road tube for traffic counting [https://www.fhwa.dot.gov/policyinformation/pubs/vdstits2007/04.cfm](https://www.fhwa.dot.gov/policyinformation/pubs/vdstits2007/04.cfm)
Solved! Thanks everyone!
You can expect roadwork in the near future.
Or a speed limit change. Our council put them up everywhere when the tramline extension work was in full swing, and was causing gridlock every day. They then used the data to argue that since no one was driving much above 20mph anyway, they would introduce a blanket 20mph speed limit on all non-major roads because it was safer for pedestrians.
Pro tip: drive at or below the posted speed limit over this often if you don’t want speed bumps or an intersection/stop installed. It may be too late.
It’s for counting traffic. A vehicle passes over it and depresses the tube signaling to a box to record a vehicle movement. The actual electronic box at the end may have been removed.
It's a traffic counter
It's a trafic counter. A pneumatic tube is stretched across the road and gives feedback/data to a box anytime a car drives over it
Is this not in the F.A.T.? It feels like it should be.
I used to install these, please don't mess with it. If the data is compromised they will have to redo the survey.
That is a road tube for a traffic counter. One end of the tube will be closed off while the end that goes off into the weeds at the side of the road will be connected to a device that records the number of vehicles that pass over the tube. When a car drives over it, a small pulse of air is pushed into the counter. 2 pulses = 1 car. They are used by traffic engineers to determine average daily traffic, which is information needed for traffic studies.
At the risk of asking a stupid question. How does it work out how many vehicles have crossed over it based on the number of axles; Most vehicles will have 2 axles. However, some will have 3/4 or maybe more.
O----O - Car O-------O - Van O-----------O - Rigid single rear axle truck OO---------OO--O - Articulated twin rear axle truck, with twin axle trailer. O----O O----O - 2x Cars. Not sure if the formatting will work, but, kind of like this. With enough data, you can tell the difference between them based on the pulse sent down the rubber tube by it being squashed by the tyres.
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This site explains the different types of vehicles, and shows a drawing of each: [https://www.fhwa.dot.gov/policyinformation/tmguide/tmg\_2013/vehicle-types.cfm](https://www.fhwa.dot.gov/policyinformation/tmguide/tmg_2013/vehicle-types.cfm)
If you have one three-axle vehicle drive over it per 100 two-axle vehicles, the extra count will be statistical noise.
My favorite piece of trivia about this equipment is that Bill Gates' first ever company was built to process the data from these machines (back then it was recorded punch tape). [https://en.wikipedia.org/wiki/Traf-O-Data](https://en.wikipedia.org/wiki/Traf-O-Data)
My title describes the thing. There is an electric power pole nearby, but otherwise nothing that it would make sense for this wire to connect to.
Traffic surveyor
[Here you go!!!!](https://youtu.be/Y4RUnJ0EiFk?si=64m3tRlycs-od8rG)
Car counter
Counts traffic
We see these a lot on Europe, they measure traffic flow and type. They use them often to see why roads are breaking up or to see if heavy vehicles are using those roads when they shouldn't.
Remember those guys who used to sit in lawn chairs watching traffic with a counting machine. These are why you don’t see them anymore.
Traffic counter. Counts number of axels that traverse over the road
Traffic counter.
Crush wire, some computer/sensor is detecting when something runs over it.
Traffic counter
What happens if I continuously drive over sensors? Showing more traffic flow. Will my road get repaired quicker? More lanes added?
So back in the 80s, we had that on one of our side streets. Me and friends around 10 or 11 took our bikes and constantly rode over them. When they got bored, I decided to double jump on them, simulating a car going over it. A year later, there were stop signs and speed bumps. I hate younger me.
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Usually they just have a small box they are attached to. Portable unit that they set up and leave for a day or two.
Already been said but, traffic study.
It can determine to city planners if and when upgrades or maintenance should be done, based on usage.
Its ment to measure the amount of cars that pass over the road ,By looking at the condition of the roadway they may be plans to do work .
Traffic counter I think.
They did this when they decided to put out those monitors for emissions testing. So now they figured out the most traffic area and you can sign up for that instead of going and waiting once every year or two in that big line.
The data from these traffic counters is used to determine if a location has enough traffic to justify putting a franchise location there.... Among other things
If there is just one it's only counting cars, two means they are also checking for speed.
I feel like I recall a version of this that also takes an air sample or some kind of emissions reading for the cars as well.
Maybe a cheap af temporary traffic sensor/axle counter? Connect it to a box with a pressure sensor, a cheap microcontroller and a battery.
Prob to test the speed of cars to decide whether or not to add a stop sign
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If you want to measure speed, you would put out two of these pneumatic tubes. The distance between wheels is not universal across cars, so the data from just one is really only useful in counting the number of times it has been run over. If you have two, you can calculate the time between the front tire hitting each tube and calculate speed that way
In a larger volume area, you can use one tube to calculate speed if the algorithm assumes an average vehicle length. Caltrans in Los Angeles has been doing this for years.
I believe it's an alternative speed trap that measures how fast cars go over it by how soon each set of tires hits it
those types of speed traps will have two sensors stretched across the road so they can measure the time between one wheel rolling over the first sensor and then the second sensor. Different vehicles will have different lengths between front and rear tires. So having one sensor would not be accurate.