I have been meaning to ask this for a while, wtf are the rubber cords connected to some sort of battery? that you see on roads? I often go over them, making a double thump and think nothing of them. Are they to track the usage of the road?
Rubber cords on road
- Thread starter bubbadu
- Start date
Yeah I thought of that too, maybe they could take the time for each tire to go over them, then setup a speed trap the next day or week. The only reason I say this is that on turnpikes I have heard that they measure the time and distance and if you go too fast, they know and give you a ticket right there.
They're called traffic tubes and they collect data about vehicles passing over them, inc traffic volume, speed (!), type of vehicle (car, truck, tractor trailer, etc), and number of axles, among some other things.
The big metal box they're connected to aren't batteries, they're heavy duty data collection computers. The batts last a good long while (months).
The big metal box they're connected to aren't batteries, they're heavy duty data collection computers. The batts last a good long while (months).
My best guess too.
The speed trap theory doesn't hold up - if they measure speed by the time interval from when your front wheels hit to the back wheels, they've got nothin. All cars have different wheelbases, so grandma tooling along at 30 mph in her Geo Metro would look like a rocket to the computer, while someone speeding like mad in his 1984 Cadillac would barely raise an eyebrow, as far as the computer's concerned.
EDIT: unless there's some way for each individual wire to get speed data from the rate the wheels pass over it, without measuring between the two...which would be seemingly impossible, due to different overall wheel diameters...
Not saying it's not possible, but I would imagine it would be VERY hard to get accurate speed data from those.
Guess again, lol. They can indeed measure speed. You'll notice that the tubes are always in sets of two. I've forgotten most of the theory, but when you install them, you must make sure that you know the exact distance between the two. You can then input that info into the data collector device (the thing that looks like a massive battery at a glance) and it will calibrate itself accordingly to be able to determine speed. As I said before, it's also able to determine number of axles, length of the wheelbase, and therefore the type of vehicle.
Tip: It doesn't work accurately if you're tailgating the vehicle in front of you
. Also, if you straddle the middle of the lanes, it has difficulty getting a reading at all. Not that it really matters. The cops don't use them, it's usually the state departments of transportation.Originally posted by: AmberClad
Guess again, lol. They can indeed measure speed. You'll notice that the tubes are always in sets of two. I've forgotten most of the theory, but when you install them, you must make sure that you know the exact distance between the two. You can then input that info into the data collector device (the thing that looks like a massive battery at a glance) and it will calibrate itself accordingly to be able to determine speed. As I said before, it's also able to determine number of axles, length of the wheelbase, and therefore the type of vehicle.
Tip: It doesn't work accurately if you're tailgating the vehicle in front of you
I've seen them in pairs, but only 1 completely crosses the road usually.
AmberClad has this one wrapped up.
Around here they use the data to calculate average speeds on the freeway and give travel time estimates. It's really very useful.
Around here they use the data to calculate average speeds on the freeway and give travel time estimates. It's really very useful.
Hmm, I'm not familiar with that configuration. I would think that that would only be capable of measuring the volume of traffic.
Also, there's another device you may have seen, they resemble big squares made out of very wide duct tape. They're used for the same purpose as the tubes.
How does it do that? Optical sensor of some sort? I can see how it would be able to determine number of axles...but wheelbases?Originally posted by: AmberClad
Guess again, lol. They can indeed measure speed. You'll notice that the tubes are always in sets of two. I've forgotten most of the theory, but when you install them, you must make sure that you know the exact distance between the two. You can then input that info into the data collector device (the thing that looks like a massive battery at a glance) and it will calibrate itself accordingly to be able to determine speed. As I said before, it's also able to determine number of axles, length of the wheelbase, and therefore the type of vehicle.
Tip: It doesn't work accurately if you're tailgating the vehicle in front of you
Hmm, not sure I can go into more detail. Like I said, I've forgotten most of the underlying theory.
It's not optical. The tubes you see are hollow inside. Depending on the usage, one of the ends of each tube may be plugged up. Any ends that are not plugged up are connected to special ports on the data computers. The computer's sensors can sense changes in the pressure from those ports. I guess from the time measurements of each axle passing over the tubes, it's able to analyze the info.
Vic
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- Jun 12, 2001
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Only when there's a pair across the road can they determine speed. Otherwise, with a single one, no. And even then you won't get a ticket or anything like that. In those cases, DOT engineers will use the data in a study to determine if the speed limit on that stretch of road should be changed or not. And yes, they can determine the weight of the vehicle (by the amount of pressure put on the tubes), and in cases where there is a pair of tubes, they can determine length of wheelbase and # of axles by measuring the time intervals.
Huh, that's kind of cool. I didn't know that. But how does it compensate for different wheel diameters - say, for example, a bus with a ~35" dia wheel, vs. a small car with a 16"? I would think that the larger wheel would take slightly longer at any given speed for the contact patch to pass completely over the tube (milliseconds) vs. the smaller one. And what if the tires are low on air, making the contact patch abnormally large - and therefore, taking longer to pass completely over the tube?
I'm not doubting you or anything, as it seems like you know a bit about these, so please don't take it the wrong way. I'm just curious.
Do they use these to survey road speeds? Some states have laws that the speed limit must be the average of what 80% of motorists drive on that road, so it wouldn't be in your best interest to slow down going over them!
Originally posted by: Black88GTA
Huh, that's kind of cool. I didn't know that. But how does it compensate for different wheel diameters - say, for example, a bus with a ~35" dia wheel, vs. a small car with a 16"? I would think that the larger wheel would take slightly longer at any given speed for the contact patch to pass completely over the tube (milliseconds) vs. the smaller one. And what if the tires are low on air, making the contact patch abnormally large - and therefore, taking longer to pass completely over the tube?
I'm not doubting you or anything, as it seems like you know a bit about these, so please don't take it the wrong way. I'm just curious.
Lol, now you're really stretching the amount of knowledge I have about these devices. Not all of the data that's gathered by the computer is "good". For properly inflated tires and high speeds, the size of the wheels doesn't make that much difference since the contact time is very small anyway. I would think that almost flat tires could indeed cause problems, but it may be that the software only registers the first time of contact for a particular axel. The computer software can do some basic error detection and determine to some extent if something doesn't look right, and it will display a hex error code for that particular set of data. Typically, when you go to analyze the data, you'll ignore the ones that had errors.
Yes, they are used to survey road speeds. Sometimes the state might decide to raise the speed limit, esp if they determine that the number of accidents isn't too high. Then they may use the devices for instance to see how much the speed limit change is impacting the average speed of vehicles. They may use that data, along with updated data for accidents to see whether they may have to lower the speeds again.
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