Yeah I know these are used for counting vehicles but can they also be used for detecting vehicle speed?
Description: two pneumatic hoses, affixed to a road. They lead to a box that’s locked to a telephone pole. Location is southern California. On a minor artery road.
Doubtful that it’s to survey if a new stop sign is needed since the next street is minor, dead ends into this one and already has a stop sign. The next intersection with another minor artery already has a stop sign.
Extremely doubtful that a traffic light is being considered since there isn’t anywhere near the amount of traffic to justify one.
This is located on a slope. Many cars speed down here. That’s why I’m wondering about speed sensing by this device.
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It’s for a traffic study. For traffic volume and speed.
Depends on the state, but it’s pretty common to to a speed study to see how traffic is flowing. This can result in adjusting the speed limit to match the majority of traffic. Or implement other traffic calming measures if a lower speed is required for some reason.
It could also lead to more enforcement I guess but where I’m from that’s not its intended purpose.
Just wanted to add that California in particular has a law requiring cities to study average speed before they change a speed limit. (And then have to pick a speed that 85% of traffic can follow, unless there are extra safety concerns.)
You can often get out of a speeding ticket thanks to this, as it’s pretty common for the traffic studies to be out of date or to have flaws that you can argue about.
Oh yeah, I’ve heard of that law. 'Sure hope they don’t raise the speed limit on this street!
Work at a city. Using these to lead to enforcement implies that city engineering is working with law enforcement and that level of coordination is… unlikely.
These kinds of lines are very engineering, very road design focused.
Also measures direction of course
In some cases they also check the axel length to determine the type of car. Not sure what that was used for.
They measure speed (how long between compression of each hose), direction (which hose was hit first), weight (how much was each hose squeezed), and axel count (how many pairs of wheels went over).
When you are calculating road wear, number of axels (and weight) is more important than number of vehicles.
You can often derive the number and type of vehicles by the pattern of “hits”. A passenger car will have a different pattern than an 18-wheeler; a van will have a longer wheelbase than a motorcycle, etc.
It blew my kond ehen i foind oit that engineers won’t even factor in cars when designing major bridges because they are essentially a rounding error compared to semi-trucks.
Kinda true. Regular cars have an Equivalent Single-Axle Load (ESAL) of 0.0004. Basically, it takes about 9,600 cars to put as much wear on the pavement as one 5-axle Semi.
Similar story for bikes and foot traffic, vs cars IIRC. You can have a staggering number of bikes and foot traffic with very light wear.
That’s the secret of Roman roads
Yes, with two hoses they are measuring count, speed, and vehicle weight. Not enforceable, as many others have said - nobody will be getting a speeding ticket from this. It’s just data collection.
Note: force measured on the hoses is a function of vehicle weight and speed. If you only have one hose, you can’t tell the difference between a light vehicle moving fast and a heavy vehicle moving slow. With 2 hoses you can now measure speed, which you can then use along with the pneumatic force to figure out weight.
They could be measuring direction also
This sent me down a rabbit hole, now I’m reading a manual on how to calculate the data.
For those interested: https://www.fhwa.dot.gov/policyinformation/pubs/pl18027_traffic_data_pocket_guide.pdf
Allow me to share some personal experiences when setting those up. Nimby’s would approach us and rant about how we were only there to justify a new stop sign or speed bump. A few times we were approached by ding dongs wielding weapons. And every once in a while people like to sabotage or steal the equipment. But once they tamper with the equipment enough times they basically get put on the shit list so their road doesn’t get serviced they don’t get plow service they don’t get anything. Maybe this was their goal maybe not who knows they’re idiots.
Honestly, highway data is used for all kinds of things but mostly for planning repairs, upgrades, and modifications. Redesigning things like intersections, traffic lights, and stop signs are rarely the result of this sort of highway data collection. It’s reported collisions and fatalities that drive safety interventions.
But again, we’re talking about nimby’s who are all fucking idiots.
Thank you for taking the time to reply. This is great information!
Would you share a story or two of your time doing this?
Sure, they’re nothing special, but they were intense at the time. Especially for a bunch of summer interns that had the misfortune of needing to find employment during a recession. I was an engineering student and my cohorts were all in the sciences as well. For being a job that required hammering, measuring, and not getting hit by traffic it was one of the more stimulating jobs I’ve ever worked.
So the typical process for us was to drive to the site, usually it was just a road segment from a list (3-5 year annually rotating lists). We had a truck bed filled with precut hoses, solar powered counting modules, spikes, and then wire mesh hose retainers. We would get the appropriate size hose, slip on retainers, hammer in the spikes, and attach and program the module.
One day a fellow in a pickem’up truck followed us from one road to the next telling us that we had no authority to be there and he would sue if we didn’t take our computers and leave. The next day, at a completely different part of the city (honestly, I have no idea how he found us) he jumped out of his truck and racked a shell in his shotgun. We all just left everything and got in the truck and drove away with him standing there shit talking. The equipment was gone but the police knew the guy. They got our stuff back. They didn’t get my buddies coffee thermos though and he was pretty bent out of shape about that. I think it was old or his dad’s or something. But never saw that guy again.
We would constantly get approached by homeless people who wanted to know what we were doing. I always tried to be as informative as possible but most of the time the basic concept was too confounding. The orange vests were always a problem. One guy asked me why I only have one cone. I still laugh about that today. Just the question. Fucking hilarious. The things you don’t think to ask. It was completely legit too. We were daily put in situations where we were inches from traffic. A single cone and a truck were the only things between oncoming traffic and our faces. Why only one cone? We had to cross roads to attach the hose on the other side. If we require a cone for traffic going this way, why don’t we require one going that way? Is the cone FOR THE TRUCK?!?
What a treasure of a memory that was.
EDIT:
I forgot, there was a contractor who did the leftover work that was occasionally needed the rest of the year, but he was always out of work during the summer and he didn’t like that. So one night I was driving past one of the modules that we set up the week before and there was a frumpy looking guy walking back to his car that was parked very near it on the sidewalk. So the next day I found out who he was from the supervisor and went to the site to check it out. He had unlocked the module and slipped in a piece of paper that just said, “you’re a removed”. Fucking ROFL.
That’s awesome, both stories! Thank you for sharing. A great day in the life.
So quick question, why do you have just one cone? 😂
Since I have neither the time nor the inclination to read it, but I do have a question- can you answer it? Quit record if you just jumped on it? Or you and like five friends?
Pretty sure it’ll be seen as noise and ignored. The algorithms aren’t perfect but they’re pretty tight and look for specific things. Unless you can emulate with a reasonable level of accuracy what is looking for it’ll just ignore what you do.
There’s a timing tolerance you can program. So if you only want to count double axles or get the speed data based on a presumed axle spacing, you can program that in. But, if you feel you must spoof it, listen to the sets of tires as they cross the hose and match that timing while stomping on the hose. You need to stomp pretty hard to get the hose to compress enough and you need to generate an air hammer pressure wave within the hose. This and the intensity is what is measured by the device and recorded as an event.
But these modules are left for weeks to months. So if the counts are all in the, let’s say, 300 range daily but then one single day shows 1000, that day’s data is typically removed from the set. Outliers can happen for all kinds of reasons (e.g. failure, hose break, weather, loss of solar power, unusual or atypical activities, children young and old). So, if the counts are wildly different than prior years’ counts, daily/weekly/monthly inconsistent, beyond comprehension, or obviously defective; they can set up more than one device if they need and some devices can receive more than one input. They can also program the device with multiple inputs to only record data within a specific range of parameters. So there are lots of ways to limit the shenanigans in the data.
And you’d be surprised at how much traffic some roads get. Even some residential roads would see thousands daily. So if you really want to bump up the priority of the road, you would be better off driving over it all day, every day until it was removed; because you’d destroy your leg trying to stomp on it that many times. And you’d have to do this on all adjacent and feeder roads to support that data. And you’d have to ensure that you do this every year until you recognize the desired effects of your endeavor, and then you’d have to continue this practice in perpetuity. Or the jig is up!
I didn’t have any inside knowledge, but I can’t think of what having two would help other than the ability to measure speed. You can count just fine with one.
I should imagine you could measure direction too, if one is tripped before the other.
They may be for calculating speed, but without any further information, there’s no way of telling what wheels belong to what vehicle, or how many wheels (edit: or more specifically, axles) a vehicle has - so it certainly wouldn’t be viable for enforcement.
You can also estimate the size of the vehicle. based on how fast it it going and the time between front and back wheel you could calculate the distance between the wheels.
with two strips you can get a lot more data than if you just have one. count, direction, speed, size, and times the road is active. I dont know if they active measure all that but its possible.
Good point about direction. I couldn’t imagine using this for enforcement, but I’m guessing you could be pretty confident any the number of axels but counting the ones that are the exact same speed and by the distance apart.
With only one, wouldn’t the length of the vehicle also be a variable?
That would be the problem for speed, but for counting you’d just look for close sets of pulses.
Oh, I somehow misread that as you saying you could get speed from just one
Ah, no, need two
I have seen cases where two tubes are used, but one only stretches half way, so they can tell which lane is used.
My question is whether they count bicycles. And are able to detect them as such.
We have these on bike lanes at intersections in the Netherlands.
In addition to everything already discussed here, they also have the role of asking for a green light automatically for you. If there are no cars travelling on Street ways contending with the bike lane, the light turns green. Alternatively, it turns green when you get your turn.
You can also ask for the green light by pushing a button, but it’s nice that some intersections (the newer ones) don’t require it.
However, I’m not sure if these can be configured to work for both cars and bikes at the same time.
The PDF doesn’t call them out specifically but I’m pretty sure with some work bikes could be figured out and identified. I’d be willing to be places with more bike traffic have already done that.
I hope so. The county I live in is extremely popular for cyclists - even in the dead of winter it’s not unusual to see people riding (sometimes I’m among them, but I have my limits). It seems like it’d be useful info for the county to have.
Agreed, and another person replied in here who sets these up that further convinces me they do. But maybe go ask that person and see what they know?
A great use of my time while I wait for my flight that’s been delayed by 5 hours!
Wait, wasn’t there something in the news recently that the airlines now have to give you money back for that kind of delay? I’m not going to look it up because you have plenty of time to. Of course they’ll probably weasel out of it anyway.
I just landed to an email with a $50 credit. The round trip was $160 so I’m happy with the credit!
Hey, yay! Welcome to wherever you are!
Thank you! I’m home, off to pick my car out of the garage and drive home.
Oof. Thoughts and prayers.
Lol thanks!
Looking at the road, it might be to make a call on which road to repair/patch in the near future based on usage if the budget doesn’t allow repairing all (it never does).
Once water gets into the cracks, things deteriorate a lot faster as the ground will push and pull asphalt around as it gets wet and dries up…
Where I’m at, there are “speed vans”, these survey boxes are also used to determine where the speed vans should be placed, though the other uses such as vehicle weight/axle count others mentioned are the main function afaik.
These speed vans are equipped with cameras that can capture several lanes and directions, from a great distance. You just drive past these things and they have a sign on top saying “your speed has been checked”.
I don’t know for sure, but I think theoretically you could calculate the time it takes between a tire driving over each line to determine the vehicle speed. I imagine that’s why there are two lines and not just one.
For sure can do speed if you know how far apart the lines are.
Probably work if distance between front and rear axle was a standardised measurement, but since it isn’t this wouldn’t be very inaccurate.
For counting or for speed? You can’t really measure speed with one because of that issue, but you easily can with two. For counting it’s probably good enough to count pulses and divide by two. Sure, some trucks have more than one axle, but it might not matter. Plus I’m guessing with enough data they have a signature of what multi-axle vehicles look like.
They’re usually not used for speed where I live. They’re simply for measuring traffic.
I can think of a few situations where it is used on small roads only to check the traffic without it necessarily meaning that any changes will be made to the small road.
If someone owns a small private road which is open to public traffic and it gets used a lot by people who don’t live on that road, it’s possible to request a reading of how much traffic passes through to determine if the municipality should take over responsibility of maintaining the road.
If there recently was built a larger bypass it makes sense to check if people still use the smaller roads instead of the bypass for whatever reason.
These things can be used to figure out lots of other stuff about traffic dependent on how and where they’re set up, but generally it’s that kind of thing. Just traffic measurement.
Speed readings would be incredibly annoying to do this way. While it is technically possible, most of the data would be useless. Sorting through data from several weeks only to be able to determine that someone probably speeded there last week doesn’t really give any meaningful information to anyone.
Speed checks are better done with the sort of doppler measurement devices that you might know from the signs that show your speed and blink when you’re speeding.
There’s almost no reason for having two of them other than to measure speed, otherwise you’d only use one. But it’s not for enforcement, it’s to see how fast most drivers actually drive the road. This can be used for things like adjusting the speed limit, or testing to see if measures need to be taken to enforce it more strictly, etc. I know there is a hill in my hometown that residents used to always complain about speeding. They used exactly this setup to track the speed of drivers. They found that there was no excess in speeding, the steep hill required more gas to maintain speed, and people generally associate louder engine noise with higher speed.
There’s two of them to determine the direction.
I always slow way down on these just to slightly skew the numbers. Though that could go good or bad for me, without a way to know.
If these had been around when I was a kid, I’d probably run over it a bunch of times with my bike. Especially going “backwards.”
It’s for traffic count. IIRC the double track to is differentiate the count between passenger cars and semi-trucks (aka tractor trailers, 18 wheelers). The double track can differentiate when there are multiple axles like you see on semi-trucks. Sometimes you want separate counts.
You could calculate speed for shits and giggles but it’s not enforceable obviously.
They generally only use a single one for counts. You use the double setup here for speed tracking.
What I’m saying is they use a double to differentiate counts between passenger cars and semi-trucks (aka tractor trailers, 18 wheelers). Sometimes you want a count of 1) passenger cars and 2) semi-trucks. That’s what I remember learning it was for. I’ll edit my previous reply in case people are misreading it.
You can do that with a single line. It’s a closed, flexible tube with a pressure sensor. Effectively a crude scale. It measures the weight on the axle. Semi trucks weigh a LOT more than passenger vehicles, even ridiculous pickups.
They are for counting vehicles. You cannot determine speed accurately without knowing the tire circumference
The circumference? Why would that matter? You have distance between the detectors and you have the time between their triggering. That’s enough to get a good estimation of the speed and direction of the triggering vehicles.
Yeah I mixed up the knowledge of how wheel size impacts speedometer accuracy with this
Whoops
By that logic, you cannot tell how fast I’m walking without my circumference.
If you know the distance between the two tubes you could determine speed and not need to know anything about the tire.
Would they be able to account for the difference in length between each axle on different vehicles?
First hit on each would be the same tire and that’s all the information needed.
That makes sense
You measure a single tire, the whole vehicle doesn’t matter.
How does the circumference matter?
It does not. Circumference only tells you speed if you’re measuring tire rotations, which this is not.
