Enforce Speed Limits With A Rusty Bike

They say you can’t manage what you can’t measure, and that certainly held true in the case of this bicycle that was used to measure the speed of cars in one Belgian neighborhood. If we understand the translation from Dutch correctly, the police were not enforcing the speed limit despite complaints. As a solution, the local citizenry built a bicycle with a radar gun that collected data which was then used to convince the police to enforce the speed limit on this road.

The bike isn’t the functional part of this build, as it doesn’t seem to have been intended to move. Rather, it was chosen because it is inconspicuous (read: rusty and not valuable) and simply housed the radar unit and electronics in a rear luggage case. The radar was specially calibrated to have less than 1% error, and ran on a deep cycle lead acid battery for around eight days. Fitting it with an Arduino-compatible shield and running some software (provided on the github page) is enough to get it up and running.

This is an impressive feat of citizen activism to provide the local police with accurate data to change a problem in a neighborhood. Not only was the technology put to good use, but the social engineering involved with hiding expensive electronics in plain sight with a rusty bicycle is a step beyond what we might have thought of as well.

Thanks to [Jo_elektro] for the tip!

37 thoughts on “Enforce Speed Limits With A Rusty Bike

  1. Some company has convinced our local council to buy a couple of speed display devices – basically a radar with a display of your speed and a smiley face if your below the limit and a sad face if your over.

    The intention is to draw your attention to the possibility you are speeding – the only trouble is the thing is more like a random number generator attached to a sensing device. Or detect a vehicle and display a number that is around the speed limit. I have never seen it display a speed that relates to my speed or that if the traffic around me.

    I hope this rusty bike works significantly better.

      1. There’s one in Milwaukee on I43 that has sensors before a slight turn on the freeway and it displays a message “too fast for turn”. I always speed up as I approach it because I want to make sure the sensor and sign are working properly.

      2. – At least in my locale, if you’re more than 10 over, they just say ‘slow down’ now, so you can’t use them to make speed runs. Seems to be a new feature in recent years.

    1. fortunately every vehicle comes pre-installed with a speed display device from the factory. if you look closely, it is tucked just underneath the steering wheel, inside a protrusion in the dash board ;)

      1. Exept those that didn’t before 1984 here in the UK as per:
        The Road Vehicles (Construction and Use) Regulations 1986,

        Also, you’re likelier to have a vehicle without a speedometer in vehicles before 1910 (as it was first patented in 1902 by someone in Germany called Otto Schulze)

    2. City of Gold Coast, Queensland, Australia have quite a number of them.
      They are quite precise for speeds OVER the limit, otherwise you just get a smile … and the smile changes its attire … with a classic Christmas hat around, well, around Christmas time.

      I found them very useful, friendly and welcomed.
      Mostly found around suburban streets with slow speeds of 50 to 30 km/h

      A lot friendlier than a revenue collection cop with a speed gun.

      1. I agree.
        Those signs are used to good effect in my area, and now instead of speed traps we have harmless speed signs which are much preferred, at least by me. I’d much rather get a friendly reminder than a ticket any day!

        In my observation, people tend to slow down almost as much in the presence of these signs as they did in the presence of a police officer, and a sign doesn’t need a paycheck (FYI: I fully support law enforcement, I just don’t think we need speed traps). I don’t know how many of the speeders just needed a reminder to slow down vs. how many are afraid that there are speed cameras inside the signs (the ones used in my area have no cameras or other ways of identifying individual speeders, but I suspect that this might be a thing elsewhere), but the darn things do seem effective at slowing people down. Also, I haven’t seen very many people panic and slam on the brakes like they do when they suddenly notice a police officer.

        1. I’m guilty of letting the spedo drift up a little over the limit, it’s not a conscious thing I’m not “lets go faster” I’m just paying attention to the road instead of staring at my spedo. I find those signs a great gentle reminder.

          I’ve found this an even bigger problem on a motorcycle, you become so focused on your surroundings and what other drivers are doing, and your speedo is even further from your line of sight.

          I know the speedlimit here is 40, I live here, but depending on how I arrived in the area it’s not uncommon to be reminded it’sn ot 45 (there’s a round about that leads into a sharp rise at one end that some times leads me to be speeding at the crest)

          Imagine if the car some how knew the speed limit (say from a box on the side of the road) and could ping you when you’re exceeding it.

    1. How else do you expect people to live so close to each other without some sort of social contract between them? how would such a social contract be enforced without the creation of an organization (the state) to enforce said contract.

      Even out of city limits there are reasonable speed limits that should be enforced, otherwise you would see an increase of resource usage outside of city limits for services that would be more efficiently used inside city limits (fire and ambulance). There is a debate on the levels and limits that allow for the most efficient use of distributed resources but as human population continues to grow and congregate in dense numbers then there will always be a need for order to be maintained in some shape or form.

      The only other option is anarchy and even though people say they would rather have it, they just haven’t thought through the consequences of their thoughts. Anarchy means that at any moment you would have to be willing to lose everything dear to you (house, family, partner, pets). The simple truth is that until human population drops back below the agrarian levels of population there will always be a need for the “state”, the thing we haven’t figured out is how to organize the running and populating that organization.

      1. Speed limits were invented as a check on over-zealous law enforcement.

        The primary speed law makes it unlawful to go faster than is safe and prudent. That led to situations where the local podunk sheriff decided that 5 mi/hr was safe and prudent if you were from out of town. So speed limits were seen as a way to say that, absent unusual circumstances, there was objectivity.

        The problem then became that the same podunk sheriffs were in charge of putting up the signs.

        The MUTCD says that for the most part speed limits should be no less than the 85th percentile speed as established by an unbiased traffic survey (which means cops in uniform holding radar guns is not an unbiased survey). Setting them lower than that usually is abusive and done to turn law enforcement into a revenue generation tool – tax by ticket.

        1. This there is what one would be called a prudent speed for the situation such as it would be dangerous to go 50 to 60mph on a neighborhood side street or downtown.
          But there is no harm done going 70mph in a 60 or 40 in a 35.

      2. The “efficient use of our resources” argument is based on the idea that YOU have some claim on all resources, and therefore get to dictate – even if in a limited sense – how they should be used and for what purposes by whom. This happens through the idea that everyone has a duty to serve other people regardless of their will – which already presupposes that such social contract exists – which means you’re begging the question.

        The idea of a social contract is fundamentally that people agree to give their freedoms away to someone else, so that this “someone else” would then decide what to do with them – and this is supposed to be preferable. Originally, that “someone” was supposed to be the sovereign tyrant, but then it got replaced by a democratically elected tyrant: the state. It’s still the argument that people can’t decide for themselves, and therefore must give up control to someone who can. Problem is, that someone is just the same people as the people who can’t decide, so the whole idea of the social contract is a paradox.

        In practice, the society is not based on a social contract that must be enforced by anyone. People largely ignore it and most people don’t even know what the rules are supposed to be, or that they’ve signed up to follow it. It’s actually based on a “moral market”, where people have individual preferences and choose to follow other peoples’ preferences in order to get other people to follow theirs. In that market, anything that can be used for haggling will be used, such as “Think of the children!”. Most people just follow along, observing what is socially acceptable, and do that to be left alone.

        Recognizing the fact, the state becomes superfluous. The people are perfectly capable of minding their own business, as individuals and groups, because they’re already doing it anyways.

      3. >The only other option is anarchy

        Much of western civilization was historically run by a concept known as “Common law”, which is a social organization that is not based on a social contract, but on case law and tradition. It rules by debate and argumentation, rather than arbitrary statutes, and it derives its power from the fact that the rulings follow common sense because they have to be justifiable to the judge and jury, and ultimately to the local population.

        Under common law, the people from vastly different backgrounds and social conditions aren’t bound by the same arbitrary “contract” that they never even signed up for.

  2. Excellent, this is just what i needed to see to compile a BOM for my community organization. There are a bunch of people concerned with the speeds on the streets in front of our elementary schools. At least this can give them data to go to the authorities with a valid complaint rather than the whimsical “people are speeding”. Although i did inform them that this wont solve the other traffic issues around the school like people stopping on the road in front of the school or people leaving the school driveway without stopping or even checking that it is safe to do so.

    1. Trouble is, if you’re not careful about the correct use of doppler radars and have a healthy dose of skepticism over the results, you’ll see a bunch of “reckless speeders” that are just pigeons flying in front of the transmitter, or the rotating fan blades of a slowly moving vehicle returning an echo through the front grille.

      (Example: the radar is set to ignore readings below 15 kph, so it ignores the stronger echo of the car, but not the weaker echo of the cooling fan which appears to be going faster.)

      Of course, if you want to incite moral panic, then by all means set up your own “gatso” box. You’ll surely prove your point.

  3. >” The radar was specially calibrated to have less than 1% error,”

    That’s actually not up to the radar itself. The datasheet for the part says 0.5% accuracy, but that’s the noise margin of the sensor itself, not the total error of the measuring setup.

    These radar guns work on the doppler principle, and the signal you get back depends on the cosine of the relative angle to the sensor. The sensor does not detect the angle of approach, so it cannot correct for this error. In other words, it reads a different speed depending on how you aim it and how far away the vehicle is along the road. It’s also susceptible to multiple echo returns which mix to give a higher frequency and result in a higher speed being reported.

    This is why the police give you a margin of doubt when they measure your speed with a handheld radar. They’re not actually that precise in use.

      1. Yes it does, because the sensor will perceive the speed as being under or over depending on the angle of approach. Generally, if you set the radar gun to the side of the road, you have to correct the numbers upwards in order to compensate for the angle, because cars that are sensed from an angle appear to be moving slower than they really are. However, the error diminishes the further down the road you go by simple geometry, so the same compensation then makes it appear as if cars further away are going over the speed limit when they’re not.

        Since you cannot place the radar directly in the path of the traffic, you have to choose between getting false negatives or false positives.

    1. Also: “Because we know that the range of the radar is 25m and because we know the speeds of the passing vehicles, we can also find out if measurements come from 1 or more vehicles and merge them approximately by vehicle.”

      No, you don’t know that. Different cars have different signal return strengths, so you can be measuring a big lorry 150 meters away, while a sleek sedan only measures at 10 meters because their radar cross-sections are different. An angled surface will return a weaker echo.

      The nominal detection range of the radar is 25 meters – the actual range will differ.

  4. And what was the 80th percentile speed they measured and how did that compare to what the speed limit actually was?

    The smart money says the limit was lower than it should have been.

  5. What about a high frame rate camera and measurement of speed from images? No RF arguments here. Seems that a good machine vision could do realtime analytics. Multiple camerae networked together. They used to have two white stripes on highways where a bear in the air with a stop watch could make meaningful legal determination and radio a unit on the ground to intercept.

      1. Thermal cameras should do the job. They can’t resolve much anything, but they’ll see the heat of the engine going across the frame, and that’s enough to calculate the speed.

  6. I’ve wanted to build something like this in my parents’ neighborhood for a long time. The tweaks I want to add would be a camera and a connection to a Twitter account. Every time someone speeds by, it would snap a picture and automatically upload it with their speed. Social shaming at its finest!

  7. Headline: Socialist Hippie-Cops use parked bicycles to speed-trap motor vehicles. How appropriate. The problem is that due to Global Warming there are so few people left who are allowed to drive cars, and those who do drive cars are the ruling Elites who have exempted themselves from the traffic laws.

  8. Quite a long time ago I designed an X Band mobile radar calibrator. It consisted of a Gunn Diode oscillator in a tuned cavity, with a horn antenna. A ten turn pot and precision regulator provided the input to a voltage-to-freq converter yielded a square wave to modulate the oscillator. If I remember correctly the scaling was roughly 3.2 kHz/100 mph. It could calibrate at quite a range! A friend noticed a speed trap way in the distance, so he pulled over to the shoulder of the L.I.E. and adjusted the pot turns counter to 80. very soon, the patrol car moved to another spot. After another round of “calibration” the patrol car got off the next exit and set up in the other direction! Oh, oops, sorry about that. Sometime after that Ku (or was it just K band?) instant on radars came out, but I never made a calibrator for that. A transponder was not that hard to design, but never built it.

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