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Homemade Speed Trap Made By Former UVA CS Professor (cvilletomorrow.org)
An anonymous reader writes: Irritated by speeders in his neighborhood and frustrated with the City of Charlottesville's inability or unwillingness to enforce the speed limit, a former professor in the Computer Science department of the University of Virginia created a program in openCV to track vehicle speed on his residential neighborhood street: "You'll find that almost 85 percent of the cars going by are violators [of the neighborhood's 25mph limit]". This includes a city bus doing 34mph.
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If everybody is speeding, maybe the speed limit is too low.
Probably not, as The Fine Article states near the top: "... installed a camera on his roof and began writing speed-monitoring software after a 12-year-old pedestrian was injured by a car last October."
Free, as in your money being freed from the confines of your account.
Authorities all over the world know that people will always go a little bit over the speed limit and hence set the limits accordingly. I know this isn't what the road safety warriors want to hear but its the truth - if they want vehicles doing around 35 authorities will set the actual limit to 30 and so on.
There is also an unwritten "grace" that is given in many areas, where you don't ticket someone until they go 10 mph above the speed limit. To get a ticket for going 34 mph in a 25 mph zone usually means you angered a cop, you were doing it in bad weather or at some other time when it was unsafe, or you wandered into a local town's legal extortion racket--excuse me, speed trap.
It is constitutionally questionable because of vagueness and due process, but it's still how driving works in a good part of the United States.
That does not mean anything if we do not know what happened or the layout of the street. Perhaps that car was speeding, but by how much? Perhaps the kid was jumping in front of the car and would have been injured anyway.
What happens in Europe is that they start making the streets in such a way that they are automatically so that you drive a lower speed. Especially in neighbourhoods where people live.
A lot of curves in the streets by placing objects in the streets., making the road more curvy and what not.
That means that the average speed will go down a lot. They just change the natural flow of traffic. and people adapt to that. Downside is that is is more expensive than placing some traffic signs and you can not generate extra income from tickets.
Don't fight for your country, if your country does not fight for you.
But the Think Of The Children campaigners will tell you that injuries to kids are X % less at 25 mph than 35 (or whatever). Which of course is a Reductio Ad Absurdum argument since you can then argue than 15mph causes less deaths than 25 etc and eventually get to the point where you end up with a 5mph limit and a man walking in front of the vehicle with a red flag and a whistle to warn people ahead. These people refuse to countenance the fact that there must be a trade off between road safety and society - which like it or not depends on motor vehicles - being able to function.
At least in California, other than the absolute maximum, and things like school zones, roads have to be surveyed periodically, and the speed limits must reflect the prevailing speed. If it is 85% near some higher number, including mass transit, then the limit is too low.
Two things about this, one, slower vehicles are much easier to avoid for careless kids and two, speed kills, every extra ten miles an hour exponentially increases the likelihood of the pedestrian being killed when hit.
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A 25 mph speed limit is unrealistic on any public road I've ever seen, with the exception of roads made of cobblestone. It's difficult to drive a modern vehicle that slowly--it takes concentration on your speed that frankly makes you have much less attention to pay to obstacles and hazards... like children.
Odd. My car drives at about that speed idling in third gear. It takes no effort at all. If I want a slower speed I pick a lower gear. It is a high volume production car with no mods.
Owl tried to think of something wise to say, but couldn't.
Utter crap. Does this mean you are not capable of driving your vehicle at 15mph or 10mph or 5mph? It must be excruciatingly difficult for you to drive at 5mph eh, god your brain must practically be hemorrhaging.
I had some kid run out in front of the car and the fact that I was only doing 15mph instead of the limit of 30mph is what stopped the kid from ending up dead or in hospital, the speed difference gave me the reaction time and stopping distance needed to avoid hitting the kid - with all of a few inches spare.
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That's all fine and good until you throw snow and ice into the mix, then all those objects become wrapped around cars and cause accidents from the excessive braking/swerving required to navigate them during inclement weather. I've lost count of how many signs and poles I've seen bent over clear to the ground after storms, or cars losing control in S-curves from the "scenic/safer" road design.
There is no necessity for you to drive fast around residential areas, you want to go fast, hit a highway or a racetrack or quit whinging, FML.
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Link to original article, name of the professor please.
If you had said 5 mph, you would have an argument. It actually is difficult to make a car go 5 mph. A lot of them won't even read their speed accurately when going that slowly. Hell, mine doesn't even indicate any speed less than 10 mph!
25, on the other hand, should be no problem whatsoever, and if it is, you should give up driving immediately and go back to walking, because you can't drive for shit.
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Last summer I wrote a python opencv program for a Raspberry Pi computer and Pi camera module. This monitors in real time. It has a lower fps due the hardware capability but does work Ok when calibrated for the distance. Here is my YouTube video https://youtu.be/eRi50BbJUro github repo is here https://github.com/pageauc/mot.... This was just done for fun after reading a forum article on the subject.
Take some discarded automotive parts (coil spring, shock absorber) and fine steel cable (the original reputedly used piano wire) and run it across the road under tension a few inches above the pavement. Go over it slowly (with the speed set by the shock absorber) and you never notice it's there. Go too fast and it slices the tire right off of the rim.
Lacking <sarcasm> tags,
that's also a problem that stems from driving too fast. but at least europeans tend to drive slower when the road conditions require it. also, these obstacles are only placed in areas, that are already low-speed (30km/h = 18mph limit). sure, you can drive arount those obstacles like a slalom-racer, but then you're violating the speed limit - and common sense - again. those limitation won't hold an idiot, but they'll give the rest of the population an incentive to think about what they are doing - and thus reducing the probability of accidents. and you'll probably avoid a surveilance state, where every "concerned" citizen uploads speed-trapping software to his webcam/smartphone, and hunts for sinners.
I suspect they hinder emergency vehicles enough to cause more deaths than loves saved.
Speed bumps do this already, and this tech seems it would do so more.
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The context was *a residential street*. Stop generalizing something which was very obviously not meant to be general, that's just intellectually dishonest. Alternatively you're suggesting that you're too stupid to realize that.
25 MPH (or 40 km/h) on a road of the quality seen in the video will usually feel like it is too slow, and it is not surprising that there are many that exceed this limit.
I notice that most arterial roads around here have the equivalent of 30 MPH (50 km/h) though reduced to 40 km/h or 25 MPH past schools. Where there also is at least one speed bump or raised pedestrian crossing (basically a speed bump with the crosswalk on top). Non-arterial roads have 30 km/h (which would correspond to 20 MPH), and there are always speed bumps.
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Those who set that speed limit are acting in reckless disregard for the safety of the public. As is that CS professor--and he should know better!
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The other main roads feeding into downtown from US 250 are High to the east and Park and McIntire to the west. All three are heavily congested for various reasons. They link to other busy roads, have shopping and commercial areas, etc
I think the solution is for the city to bite the bullet and install speed bumps. It will not be a popular measure, but that is because people want to speed through there to get into or out of the downtown area. Too bad, just plan a little further ahead.
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Which has f' all to do with the fact that a car travelling at 20mph is not likely to kill someone it hits and a car travelling at 30mph is massively more likely to kill anyone it hits.
I see nothing in your calculation about the probability of brain damage or death from high speed collisions.
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"You'll find that almost 85 percent of the cars going by are violators"
Then your speed limit is set too low, unless there is some compelling reason for it to be that low speed limits should be set by the average traffic speed (within reason). I think my state even has a law to that effect.
Does this mean you are not capable of driving your vehicle at 15mph or 10mph or 5mph?
My last car had an engine idle speed around 7-8mph, meaning it was not possible to drive 5mph at all. Simply letting up on the break and not touching the gas at all would result in the car moving faster than 5.
It was also not possible to consistently drive 10mph, as the slightest touch of the gas pedal would cause the car to accelerate to just over that speed.
Mind you that doesn't mean I couldn't abide by a 10mph speed limit, it just means I can't do so while driving AT that limit, I have to not touch the gas and let the engine pull the car along at idle speed just a touch under 10.
However where I live the lowest posted limit on a public road that I've ever seen is 25mph, including the road I live on.
I have seen 10mph limit signs at a mall parking lot once, and fair enough since anywhere in the lot where there was people walking idle speed was about the safest one could move at, but I've never seen 10 (or even 5) posted on a public road before so all of this has never really been an issue.
(Not to mention I don't own that car anymore)
What happens in Europe is that they start making the streets in such a way that they are automatically so that you drive a lower speed. Especially in neighbourhoods where people live.
I live there. What happens in practice, is that the people that were already obeying the speed limit are slowed down. And the people that were speeding before, see it as an obstacle course challenge, going as fast or faster as before, but now also swerving dangerously... Also, when you put a big obstacle on the road, people tend to focus on that, instead of watching out for pedestrians.
Where I live, there's a sudden road divider and recombiner intended to slow drivers down from a 40mph zone to a 25mph zone. But every part of the street is well lit with overhead lamps except this road obstacle. There are always dark tire marks on the curbs there.
So set speed limits at 10mph, or 5mph, or ban cars entirely if decreasing fatalities is always a justification for decreasing a speed limit, because if it isn't then you need a more credible case.
In the UK the normal speed limit in a residential area is 30mph. 20mph limits in the vicinity of schools are becoming more common. In general UK speed limits are quite relaxed, and especially on non-urban roads policing of moderate speeding is very limited; It is not at all unusual to find traffic averaging 80+mph on UK motorways (interstates) which have a 70mph limit, and you could comfortably do 90mph if traffic is flowing with no real risk of a ticket.
All of this should make the UK a very dangerous place for pedestrians if speed limits alone were a primary driver of road fatalities, but they aren't. The UK averages 3.6 fatalities per billion kilometres driven. The US average (where limits are on average lower) is 7.1, which is effectively double. It seems much more likely that issues like car quality, driver certification, road design, car design etc are far more influential.
Speed limits should be set based on the first only. The entire objective is reduce the probability of and accident to an acceptable level, not reduce it's severity.
Yeah - my seatbelts, crumple zone, side impact airbags, front impact airbags, passenger airbags, re-enforced pillars, side impact beams, automatic roll shut off, bumpers, safety glass, etc. all are very helpful at reducing the probability of an accident. That's a seriously wrong statement.
There's only one speed which is safe for adequately careless kids. 0. Anecdote. Two weeks ago I was driving home. There were a lot of cars on the side of the roads and my neighborhood has a lot of kids so though the speed limit is 25, I was doing somewhere between 10 and 15. And then right out in front of me shoots a kid out of the driveway in a gokart, he hits the road spins out and stops right in front of my car. Barely stopped in time, and had I been 1 second sooner, that kid would have been run over. He rights himself and tears off in his gokart doing about 20 mph down the street. I'm lucky I was 1 second later because no amount of careful driving would avoid an incident like that because with people with effed up views of driving like yourself, had it gone to court you'd have probably found me at fault.
Anyone that speeds in a residential area is the worst type of scumbag.
On an open highway, go for it, I think we should be allowed to go 100mph. Driving around people and kids only a few feet from their homes, they need a punch in the face to go along with the ticket.
Do not look at laser with remaining good eye.
(Unless the law has changed...) California law says that if a high percentage (like 85%) of drivers go at or above a certain speed, then that speed is what the speed limit should be, regardless of the signage.
There was a case in Palo Alto about 25 years ago where the police set up a speed trap on Embarcadero between the 101 freeway and El Camino and one of the drivers caught in it paid to have the traffic monitored (without police presence which obviously influences drivers) and proved that he had been driving at the same speed as most of the traffic. Somehow the driver knew that the law said that most drivers have a natural sense for what is a safe speed and will drive in a safe manner and that speed is allowed.
All of this should make the UK a very dangerous place for pedestrians if speed limits alone were a primary driver of road fatalities, but they aren't. The UK averages 3.6 fatalities per billion kilometres driven. The US average (where limits are on average lower) is 7.1, which is effectively double. It seems much more likely that issues like car quality, driver certification, road design, car design etc are far more influential.
I would say that the UK is much more pedestrian friendly than the US in general. Just one example is the use of zebra crossings. Also the level of driver education is higher in the UK, in my experience.
Japan started painting fake little pyramid shaped obstacles in the road. Being flat paint they don't annoy you like speed bumps, but they are quite effective at slowing down traffic. Some other east Asian and European countries have started adopting them (IIRC Denmark was one of them).
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If he goes to the PD and files a complaint with the recorded evidence the PD has no choice other than writing a ticket for every violation. It is handy for bicyclists to know this as with a cam mounted on the handlebars, one can get the plate number of every car that tries to pass you in the same lane or in a no passing zone.
Speed limits should be set based on the first only. The entire objective is reduce the probability of and accident to an acceptable level, not reduce it's severity.
Yeah - my seatbelts, crumple zone, side impact airbags, front impact airbags, passenger airbags, re-enforced pillars, side impact beams, automatic roll shut off, bumpers, safety glass, etc. all are very helpful at reducing the probability of an accident. That's a seriously wrong statement.
None of those items has anything to do with how speed limits are set.
I don't disagree with your point, but you're conflating a bunch of numbers which aren't really comparable.
1) Motor vehicle fatality rate doesn't tell you much about pedestrian fatality rate.
2) Driving distances area greater n the U.S. so those billion kilometers driven are not comparable. Dividing the fatalities per 100,000 inhabitants by fatalities per billion km yields 8100 km/inhabitant per year in the UK, versus 14,900 km/inhabitant per year in the U.S. So the average American travels 84% further each year than the average UK citizen. Most likely, a greater percentage of those U.S. miles are at higher speeds on highways where accidents are more likely to be fatal.
The problem at speeds higher than about 50 mph is physics. Given how bodies strapped inside a car react in a crash, 50 mph is about the point where internal organs and blood vessels start tearing apart from their own momentum in a crash. At 100 mph, accidents are almost always fatal for the same reason (energy that goes into tearing up your internal organs is 4x more than at 50 mph). So a disproportionate number of traffic fatalities come from these higher speed accidents. In other words, a single stat like fatalities per billion passenger km doesn't give you the complete picture. You need to control for traffic speed distribution within those billion km first just determine if there's any blame left over to be assigned to other factors like car quality, driver certification, road design, car design, etc.
Exponential function is not the same as an exponential relationship. You're using the term "exponential function" as equivalent to exponential.
I don't know I lived in New England my entire life and I've never had any of the troubles you mention on snow and ice. With all wheel drive, modern snow tires, keeping you speed somewhat reasonable and engine breaking its pretty hard to slide off the road or not make it up a hill.
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the term "exponentially" is being abused.
No. Unless you're talking about x^1, exponentially is not being abused. What else are you going to call it? Linear? What's your threshold for exponential? x^3?
So it's true...all the nerds really have abandoned Slashdot. We now have a place where the parent comment, which a high-school algebra student should recognize as foolish, gets modded "Insightful". I think I've finally had enough of this place.
So where do the cool kids hang out now? Oh my god, look who I'm asking!
For the record: x^2 is quadratic, x^3 cubic, x^4 quartic, etc., c^x is expontential
Like I already said, I don't drive at the limit when it is that low...
Not sure why you felt the need to tell me to do what I literally just said I already do, but thanks for the accusation anyway.