Here's a surprising anecdote I've discovered living in South Africa wrt traffic lights.
When they're not working at a busy intersection in my area, the intersection effectively becomes a four way stop. And I've found that as long as everybody follows the rules, traffic actually seems to flow FASTER than when the traffic lights are actually operable.
I see so many places that could have roundabouts instead of lights. Plus, if the maximum speed inside my town was lowered to 40km/h, we could have shorter yellows. You can never reach the 60km/h limit for more than a few seconds anyway.
Speaking for Johannesburg, we can't have shorter yellows because too many people treat them is "last chance to speed up to make it through before it's red for too long!" and JMPD is beyond useless at law enforcement.
Where I live they've been actively removing traffic lights. One strategy is to turn multi-lane roads into single-lane ones with a lower speed limit, and crossing islands for cyclists and pedestrians. Cars move slower, but more consistently, traffic is better able to self-regulate, so while I haven't timed it, I'm fairly sure traffic is actually moving faster despite driving at lower speeds.
Of course, it helps that infrastructure adjustments over the decades ensures that many people that don't need to be in cars, aren't in cars.
Sounds like you're living in a country where local government actually cares to improve things rather than doing as little work as possible while also self-enriching themselves as much as possible.
There's plenty to criticise at all levels of government here, but overall I indeed am pretty satisfied with my local government. And on the infrastructure level especially - whenever there are roadworks, they're annoying, but I'm always looking forward to what it'll end up as.
If the lights are at an intersection where a very busy road crosses with a less busy road then turning it into a four way stop just turns it into a traffic jam on the very busy road. I’ve seen this happen during rush hour in the United States multiple times.
When it’s not rush hour though maybe the situation is different? Not sure.
Seriously though, speaking as a South African living basically next to Sandton, there are plenty of traffic lights near to me which cause complete chaos when they are out. They will cause significant delay for the entire working day on certain routes, e.g. anywhere on Winnie Mandela (formerly William Nicol) Drive.
There is however one intersection (Stirling and Balmoral Ave) on the way to my kid's school on a non-major road which definitely works better when its traffic light is out, and this is at any time of day in my experience.
Some traffic lights definitely should rather be mini traffic circles, e.g. on Peter Place by the one office park and had the exact same frustration for the one on Grosvenor Road near to Bryanpark.
As the Johannesburg Road Agency (like all City of Johannesburg Municipal companies) is so incredibly incompetent, our traffic lights are incredibly unreliable, I shudder to think how much it sucks out of our economic output all the people sitting in traffic longer than is needed simply due to an out of order traffic light.
And the local police also don't help with regular roadblocks while at the same time being terrible at law enforcement (yes, you'd think roadblocks are a sign of law enforcement, in practice though they're more for soliciting bribes while screwing up traffic).
The two-adjacent signals causing extra traffic is something I encounter daily in Berkeley -- Ashby / Claremont & Ashby / Domingo. I probably blow an average of 5 minutes a day cause of that double intersection.
To highlight one other point from the video: You want a light to be able to clear the line built up each time. If not, flux in > flux out and that's a recipe for a growing line, which causes a traffic jam.
They are very common all down the SF Peninsula because of the Caltrain tracks. There's California/Carolan all through Burlingame (which has some of the most dangerous train crossings in the country because you can get stuck on the tracks between the lights), and then it follows El Camino on one side while the other one goes from Delaware (San Mateo) to Old County (San Mateo / Belmont / San Carlos) to Alma (Palo Alto) to Central Expressway (Mountain View / Sunnyvale).
The Old County lights at least are staggered so they are almost always green at the same time. The Central Expressway ones, not so much - there've been times I've been stuck for 20 minutes trying to cross the 100 feet from Moffett to Castro in Mountain View, because the light timing never lined up with the train signals.
> there've been times I've been stuck for 20 minutes trying to cross the 100 feet from Moffett to Castro in Mountain View, because the light timing never lined up with the train signals.
They've conveniently solved this by closing the Moffett->Castro side of that intersection entirely. You can still go Castro->Moffett, but they're planning on closing that to eliminate the grade crossing entirely.
Oh, nice. So all traffic is routed over Shoreline and then enters downtown through Villa/Dana? That's a better road for it anyway, with the grade-separated Caltrain & Central Expressway crossings.
Is there still pedestrian access from the northeast side of the Caltrain? I used to live in the Moffett/Middlefield area and being able to walk to downtown was a big draw for that.
> So all traffic is routed over Shoreline and then enters downtown through Villa/Dana?
Yeah, they're planning to put a ramp from the Shoreline bridge over the tracks down to Evelyn to spread out the traffic, but right now people take Villa.
> Is there still pedestrian access from the northeast side of the Caltrain?
Yeah, all the crosswalks are still operational. The long term plan is to put a bike/ped tunnel under Central and to completely close off the Castro/Caltrain side.
Many progressive cities intentionally time their lights for this for two reasons. One is to intentionally limit capacity. Once a road gets past a certain density, you end up with problems that make things astronomically worse (for example: people who "block the box" and cause everything to grind to a halt.)
The second reason: trying to incentivize people onto trains, buses, bikes, foot, etc.
Cambridge, MA does this. The light are purposefully timed to not let you travel through multiple greens on the tertiary roads in particular, less so secondary, etc.
Cambridge also gives a substantial amount of time to pedestrians as part of every cycle- no "beg button", because the city does not consider someone on foot to be less deserving of crossing time - specifically to not have the car "be king". By making it relatively fast to get around on foot, they reduce the incentive to drive.
They also heavily structure the residential neighborhood streets with one-way directions designed to make it very difficult to use the streets people live on as cut-throughs when the main roads jam up because that leads to noise, pollution, and danger to people on foot and bike, particularly because the kind of person to use a neighborhood as a cut-through is likely also driving quickly and aggressively.
Exactly, a road system as a whole has a certain capacity and friction in the system is used intentionally to maintain order. It is a bit like limiting electrical current using resistors in electrical circuits. Sure you could leave them out, but then you will have problems.
> You want a light to be able to clear the line built up each time
Ideally, yes, practically, no. In reality you also have to consider what comes downstream of a traffic light. It doesn't help at all if one traffic light has perfect throughput only to put everything into gridlock in the next node.
That means in most real traffic systems each intersection lane will have to have less then ideal throughput because you don't want to overwhelm the next section, as this could be even worse for the system overall.
If you have some engineering background you can also think about this as impedance matching. If you have a 4 lane road narrowing to 2 lanes you have a sudden impedance increase, leading to flow issues. If you put an intersection inbetween you now have a way to manage that impedance mismatch with signaling times, but you have to both look at the impedance before and after the intersection.
I'm sure AI can figure this out better than a human can. Obvious and empirical, we certainly haven't figured it out or optimized it, with all the engineers that CalTrans has. How often have we been in a four-way controlled intersection and the green is on for the empty side. There's no way that's impedance matching, it's more like Good to go boss, call it a day.
There's no incentive to modernize traffic light control because it's public works and there's no capital profit motive for it in the same extent as private. I would not advocate privatizing it either because that will bring different consequences. The hero will be that new young Caltrans engineer who's grown up in the AI generation and will probably be fed up with the legacy technology.
> How often have we been in a four-way controlled intersection and the green is on for the empty side. There's no way that's impedance matching
Who claimed it was tho? We were talking about throughput. If all your intersection knows is time, it can't decide based on traffic. Which is why inductive loops, camera based systems and so on exist, but (1) they are not deployed everywhere and (2) if they are deployed there may still be a time based limit for the case of defective sensors.
Our traffic systems are already pretty well optimized where we are willing to spend money on them. Note however that if you 100% optimize any system for perfect throughput, it has zero slack to deal with unexpected fluctuations in traffic patterns. That is as true for traffic as it is for networks. Throughput is important, but so is comfort, resilience, predictability and cost. All different metrics you have to keep in mind¹ and all of them can suffer when you over-optimize for one.
The view from inside the traffic that we are part of may make that seem inefficient, but seen system wide the main problems usually are not traffic lights, but harder to change structural issues.
¹: or rather you don't have to keep them in mind, since there are people who specialize on just that and are pretty good at it
One thing that I noticed about traffic lights in CA -- there will be like 4-5 cars who are driving on the major road and approaching the traffic light. Then a car arrived from the small road at the intersection. The traffic light will then turn red for cars on the major road, so all 4-5 cars will brake and stop at the light. The small car proceed to turn left into the major road. A few seconds later, the light for the major road turns green again and the 4-5 cars proceed.
I have seen this so often that I sometimes wonder if it'd be more fuel efficient to let the 4-5 cars on the major roadway proceed (the traffic lights have cameras anyway) while letting the one car from the small street wait slightly longer or wait for a fixed amount of time.
I wonder if there's any traffic engineer on HN from California and if so, I'd love to hear an explanation/rationale behind the current approach.
I live in BC near a highway intersection and in my experience they seem to do what you suggest.
I approach from my street and if the highway is empty, almost instant green. Otherwise I have to wait some time until the road clears. During peak hours when the road doesn’t clear, it just seems to go green after a fixed time.
My son and I observed similar behaviour at a puffin crossing on the way to his school, and we’re buildng a model of it using an Arduino Uno with a RCWL-0516.
I'm in the US and I just spent 5 minutes trying to figure out why a bird that can fly needed a special road crossing. I mean, a penguin crossing might make sense in a few places (but not Antarctica because there are no cars or streets there). Where do they have puffins that need to walk across a road?
I used to live in a south Florida (Miami) suburb and the traffic lights there function like what you suggest too. So after moving back to southern CA, it's something I had to adjust (and the traffic light behavior difference became obvious to me).
Historically, the amount of data available to traffic lights controllers was rather rudimentary, basically a simple presence/occupancy detector covering the area immediately upstream of the stop line and/or some point somewhat (a few seconds of driving time) further upstream of the stop line and/or the whole area in-between. The detector could be implemented via an inductive loop buried within the pavement, or it could be a camera, but with the camera still usually working only as a simple presence detector with no advanced detection capabilities where it could actually intelligently "see" individual vehicles.
With such a setup, the traffic lights controller can't actually see that there's only 4-5 cars approaching on the main road – either they're far away enough that they don't even register on the detector for the main road yet (in which case a vehicle waiting on the crossroad will naturally trigger the phase change without delay), or even if they're already near enough to the intersection to trigger the detector, the traffic lights controller can't actually know that it's "only" 4-5 vehicles and its strategy might hence be that if the main road has had more than x seconds of uninterrupted green time, a demand from the side street will be granted immediately, regardless of traffic conditions.
With a state-of-the-art system it'd be different – with more and better sensors the traffic lights controller could actually track individual vehicles (or platoons of vehicles) as they approach the intersection and try making the kinds of trade-off you mention – but somebody needs to pay for that kind of upgrade. (And I suspect we haven't necessarily reached the point where the price premium for that kind of advanced traffic lights controlled compared to classic traffic actuation is negligible enough for it to be the default at least for all new intersections and equipment renewals, either…)
Reminds me a bit of the MIT study that relates to spacing in densely packed roadways [1]. Whenever I apply the rule (look into my rear view mirror and decide how late to slow down), I feel like a good little molecule in an ideal gas.
Better not, it would just get me even more pissed off at how crude and incompetent German traffic engineering is. Pretty sure some frustrated worker is making it worse on purpose - you don't reach certain peaks of crappiness accidentally, it takes _work_.
Can't speak to Germany, but one thing I like in the Netherlands is that if you approach an empty intersection the light will automatically turn green for you. Have never seen anything like that in North America.
And the roads themselves are good in NL (huge contrast when I moved to Montreal, where we'd have a metal mesh underneath bridges to catch falling concrete)
According to Claude, NL only has 5500-6000 signaled intersections and of those approximately 900-1450 are of the type you are suggesting (iVRI). The benefit is also higher in NL due to the density and amount of cyclists. iVRI is also not latency sensitive and so installation costs are low as signaling can traverse the regular cellular network.
In the US, we have many more lights due to the road layout (grid). There are more than 3200 signaled intersections in my county in California alone despite being 1/14th of the land area of the NL.
The robot also estimates that there are 300,000 signaled intersections in the US. We honestly don't know how many there are because they are all operated by different agencies.
For US arterial roads iVRI has limited benefit. So the focus in the US has been on V2X development which focuses more on crash avoidance and has much higher installation costs due to latency requirements. In the end there's a lot of low hanging fruit here in the US if signals could just be retimed.
NL has one procurement entity. In the US there is no single coordinating entity to standardize traffic lights. Each state standardizes its own lights and then each municipality handles its own procurement.
I don't know the numbers, but I live in NL and I can't recall the last time I encountered a traffic light that just runs on a timer; as far as I know just about all traffic lights have some awareness of traffic.
Lowering the number of traffic lights in and of itself is a good idea. Overpasses and (turbo)roundabouts, clever right of way, better road hierarchy; there are lots of alternatives that may provide better throughput and more safety for a given intersection.
The Netherlands as a country with 18M inhabitants is best compared to a big city with the surrounding metro area.
It happens in the US but is rare. Mostly it's a road servicing a well connected person or wealthy neighborhood that gets the dwell time reduced to nearly nothing.
There's an annoying one near me at the bottom of a hill where anyone approaching from the sidestreet will ruin the descent on bicycle, even if they were turning right (from a dedicated turn lane) and didn't need the light to change for them at all. Another is a former police station now used as a park facility. Cars entering the parking lot only need to barely brush over the sensor and the light changes instantly for no reason because they never reprogrammed the light when the police left.
> you don't reach certain peaks of crappiness accidentally, it takes _work_.
Have you really never seen what happens when something grows organically without global maintenance? Not saying that this is what happened in Germany, but "it takes work" sounds naive.
It doesn't take work to write a crappy codebase: all you have to do is add code without really caring about the overall architecture.
Or said differently, if you can fix the German traffic engineering, you should apply there because I'm sure they would be happy to have an easy and perfect solution.
What's your issue with traffic in Germany? I know it depends on the city/state, but it always seemed pretty okay to me (though I haven't been driving much in other countries, so I don't have that much experience with "better" systems)
From what I've seen about US traffic, there doesn't seem to be much to be envy of.
> Actuated signal control [...] inductive loop sensors embedded into the road surface
It blows my mind how many people don't realize that's what those circles near the stop bar of an intersection are for, and will then stop 3+ car lengths behind the stop bar, and then can't figure out why the light is never going green.
> two signals closely spaced in a row on a major roadway. If one signal gives a green but the next one doesn’t, cars can back up
This is a major problem at an intersection near me that I used to have to drive through frequently. Two intersections, only about 500 feet between them, and MOST traffic during rush out coming from just one of the directions, yet the lights were often exactly out of sync. The first light would be red while the next one was green. Then the first would go green while the other went red, and traffic would only move about 500 feet then stop for 2 minutes. The backup would last well over a mile.
> The obvious next step in efficiency is coordination of most or all the signals within a traffic network. This is the job of adaptive signal control technologies, or ASCT. [..] These types of systems can dramatically reduce congestion
My cynical ass would not be surprised at all if oil/gas companies were lobbying against ASCT because idling cars are buying more fuel. Wouldn't be too hard to convince people that an ASCT would cost too much to implement while not producing significant traffic benefits.
> This is a major problem at an intersection near me that I used to have to drive through frequently. Two intersections, only about 500 feet between them
In San Francisco (as well as other cities I've lived in) they put police in the middle of intersections during rush hour to guide traffic (i.e., stop cars before they drive into an intersection that they'll get stuck in the middle of). Seems woefully inefficient
When traffic is really heavy humans are better than machines at getting traffic through. However they cost a lot of money and so are only rarely worth the cost.
It might be more about drivers respecting the signals than about the efficiency at which the signals are handed out. Plenty of people will try to squeeze into a yellow light even if they might get stuck on the intersection if the road is backed up but they are less likely to do so with a police officer watching them.
There is that, but also the police can see that the road will backup and stop traffic before that happens. They let someone who is going to a non-backed up road go instead. They also can see a road is backing up and give that high priority if there is a place for the cars to go.
Curious...in the UK, is the implementation of something like that done by government employees?
In the USA, a significant amount of tax-funded infrastructure is actually built out by contractors, which means there's profit going to a corporation, and there's often a cynical idea that the contracts go out to whoever will send a kickback in the form of a campaign contribution to whoever makes the decision on which contractor to use.
The local councils (local Authority) usually get external companies to design the systems, but there are standard, off the shelf solutions that are specified to be used. These systems range from time synced junctions (with Vehicle attenuation) up to full Urban Traffic Control systems, the protocols used are mostly standard (UTMC), so the local Authority just needs to say what they need. For a UTC system it used to be that the council would run the instation, but with cloud computing, that's mostly run for them now as a hosted system. Usually this is all controlled by the standard local council procurement rules, and run by council employees not elected officials. The elected officials can say a scheme is needed and approve costs, but not who does it.
If I had a nickle for every time I’ve had to get out of my car and walk up to the person in front of me and explain that they need to pull forward for the light to change - I’d have two nickels, yadda yadda yadda.
> My cynical ass would not be surprised at all if oil/gas companies were lobbying against ASCT because idling cars are buying more fuel. Wouldn't be too hard to convince people that an ASCT would cost too much to implement while not producing significant traffic benefits.
I don't think you need a vast conspiracy to point out that connecting traffic signals costs more (fancier signal equipment, running cable, maintaining the cables, etc) and the benefits may be subtle, hard to predict, and maybe even hard to measure.
Additionally, you have a lot of people that would prefer to slow traffic. Depending on local culture, investing in traffic control can be difficult (although upgrading traffic signal systems may be better able to accomodate priority for transit and bicycle detection)
Back when I rode I had to add a giant hunk of iron to the bottom of my motorcycle so these fuckin things could see me. Sometimes that still isn't enough and after a few minutes of shimmying back and forth over it I'd just run the red
There's a major arterial near my house. One day, the power went out in the area, and the traffic lights went dead. I discovered to my amusement that throughput on the arterial and its crossings increased dramatically, as drivers simply cooperated with each other.
There are already cameras on top of all the lights. How hard can it be to hook them up to AI that is instructed to maximize throughput? The current system will block 3 directions while having a green light on the 4th which has no traffic.
I once complained to a friend about this, and he told me that the traffic engineers were experts and I was lying. The next day I was driving on that road, and got a red light. You could see on down the distance 3 greens. There was no other traffic, and no cross traffic. So I sent him a photo. He conceded :-)
I guess the main reason traffic lights exist is to avoid incidents, not necessarily to maximize throughput. Maximizing throughput is just a nice no have, and so no one bothers. Just a guess though, I've no idea what I'm talking about.
> How hard can it be to hook them up to AI that is instructed to maximize throughput? The current system will block 3 directions while having a green light on the 4th which has no traffic.
You don't need AI for that, you just need the system configured properly. Lights near my parents' house have been running cycles adapted to actual traffic for at least two decades, probably three... although using inductive loops in pavement rather than cameras.
There are reasons you might want a short green every so often even with no detected traffic... it would help manage worst case situations for a stuck open detector, etc. But those wasted greens shouldn't be long enough to notice. You might also have situations where locally suboptimal behaviors improves performance or safety elsewhere and that may lead to a better overall system results. I'm not claiming this is the situation in your scenario, but it can explain some negative experiences.
I've certainly seen it in places... There's routes I drove where if you had a green and you keep within narrow speed ranges, you get greens, and if you go at the inbetween speeds, you get reds. Some of those might not be 100% consistent if something interrupts the regular cycle like a pedestrian crossing or an emergency vehicle.
Otoh, Milwaukee circa 2003 had all the lights on a schedule. Every intersection made the same changes every day. Super frustrating when I was consistently slow to get out of the house for a scheduled pickup and missed the light everytime.
> There are already cameras on top of all the lights.
Those are infrared sensors that pick up the heat from car engines. They've had to be modified to pick up electric cars.
> How hard can it be to hook them up to AI that is instructed to maximize throughput?
The equipment cabinet at the intersection has been engineered to prevent all sorts of fatal things that happened in the past. Such as one set of relays being stuck so that one direction always gets a green light while the other direction gets red/yellow/green. They're designed so that can never happen again (when "broken", you'll see blinking red in all directions).
The controllers need to be standardized so that you don't need experts to be able to diagnose & repair them. They also need to be certified. It is not possible to certify an expert system (or as they're now called "AI") because it is not possible to use formal methods to prove correctness.
> The current system will block 3 directions while having a green light on the 4th which has no traffic.
That specific intersection is set on a timer. For a single, 2-lane each way, non-complicated intersection, it can cost $100k for the lights, poles, sensors and equipment cabinet. Every wire is underground in pipes so that the expansion of concrete in weather won't stretch/break the wires.
> as drivers simply cooperated with each other.
That's something that most people learn in kindergarten: "share with others" and "take turns".
Where I live (fly-over country), when the power is out, traffic backs up significantly.
Disclaimer: I used to work for my state's combination DMV & highway department.
Actual "Expert systems" could in principle get certified because they have explicable behaviour. The juice isn't worth the squeeze but it could be done. However the LLMs do not, we don't really know why this does anything even vaguely useful and we can't say if it might fail, or how we'd know. Useless.
I'm sorry, but that all sounds like excuses. None of it looks like it should impede using AI-developed algorithms.
Heck, an AI isn't even needed. A simple cost function could be easily developed, where each car accrues priority as it waits, and the lights go green on the ones with the highest priority.
I used to work at a traffic signal controller company. We were under strict orders not to use AI. We did anyway, in a simulation, and let it optimize over the weekend. When we got back it had blown all of our previous attempts out of the water. We huddled around my coworker's workstation eager to see its masterful new pattern. It just made one phase red all the time and one phase green all the time, effectively closing one road. The throughput on the other road was through the roof though, since its light was always green. We did not present these results to the boss.
A lot of lights exist not to add throughput, but to replace 2-way stops where less performant traffic (so like idiots, grandmas and heavy trucks) would have problems getting in, say fuggit (or get honked at, get flustered) and cause a near miss at least.
Yeah, my city traffic engineer is an ass too. There was an intersection I went through every time I left my old house. Outside of rush hour, it functioned much better as a four-way stop than a signalled intersection. I pointed this out and he said “that is inappropriate for two arterials”. Um, I live there. You don’t.
I always thought that traffic signals should be trying to minimize squared anger, where anger increases linearly with time spent waiting at intersection.
one thing that drives me nuts is a left turn arrow that isn't long enough to clear all the cars waiting in the left turn lane. So often, it would only need another 5-10 seconds but it seems to have a limit that it can't exceed. This leads to frustrated drivers trying to squeeze through on the yellow light or even the red.
Also red left turn signals should not be a thing. If there's a gap in the oncoming traffic you should be allowed to turn left across it as long as the straight-ahead traffic has a green light.
Where I live (in the PNW) they mostly are not a thing any more. The only ones remaining are there because the combination of sight line and traffic speed makes them too dangerous to turn into flashing yellow. Not sure if that has spread to other regions, but I would guess it is heading towards being universal pretty quickly.
The only possible second-or-third order effect of red cross-traffic arrows is to decrease the downstream traffic on the cross road. Mostly, the places where I encounter them have a low traffic cross road. IMHO, in those situations, red cross-traffic arrows are simply a failed "traffic engineering fad".
(Edited to fix a typo and generalize "red left-arrow" to "red cross-traffic arrow" to account for left-side-of-the-road driving systems.)
I'll grant that it might be safer for pedestrians, as then they only have to watch for right-turning traffic and not people turning left from the opposite side of the road. There are a lot of intersections that rarely see pedestrian traffic though.
I live in a small city in rural area (Nevada City/Nevada County, ca).
Traffic lights here are unbearable. The situation, as I understand it, is that there's tradeoff between through-put and latency. Basically, if you make each cycle of a light really long, like 1-2 minutes, then how many cars get through, can be maximize. Sounds good but such optimizations drive the average driver f---kin nut. I don't think that cost should be ignored.
>As sensors become more ubiquitous and computing power increases, traffic management may slowly but surely be relegated from civil engineers to software developers and data scientists. But, that also means that ASCT systems may be more vulnerable to security threats, a scary thought if they’re controlling the signals for an entire city.
I feel like software engineers would write more secure software than civil engineers. It would be the opposite. I'm also not scared that much of someone controlling traffic lights. It's already possible using emergency lights.
ASTC systems do not "dramatically reduce congestion." They result in a small (probably single digits) increase in traffic flow at best, which is a rounding error. God, I'm sick of this dude's flyover videos and him being treated like some genius.
Numerous cities don't bother with ASTC systems because they a)don't do very much yet cost a lot of money in equipment and staffing, and b)just further incentivize low occupant vehicle traffic, which is just about the lowest priority in most cities these days because that in turn creates more traffic. If there was one overarching tenet to traffic engineering and urban transportation planning, it's that you cannot solve traffic by building more roads. It doesn't work. It has never worked.
Traffic is something 99% of the population thinks they understand because they sit in it, see it, etc. and probably 95% don't have the foggiest idea how it actually works, and merely have a severely uneducated and highly biased personal opinion. And boy howdy, do they hate bike lanes and bus lanes.
Adding (or removing) a lane does not even remotely have a direct correlation to maximum traffic flow. If you have a three lane road and you make one lane a bus or bike or bus-and-bike lane, you do not lose 1/3rd the traffic flow capacity. It's dramatically less than that.
By making bus transit faster (where each bus holds ~60 people...) and biking safer, not only do you actually reduce traffic, but you also provide emergency vehicles with a faster route through traffic.
In Paris more people travel by bicycle than car. That was a direct result of Paris heavily restricting motor vehicle traffic through the center.
Every person on a bicycle is one less person causing noise, pollution, congestion, wear to the road, danger to others, and using (at least) one less parking space (because you don't just need a place to put the car where it is kept, you also need space for where it is going.)
Simcity designers initially based Simcity off actual real-world stats and planning figures. They had to throw out the figures for parking and road capacity because otherwise the game would have looked like nothing but roads and parking lots.
What I find most interesting about the computer side of traffic signal controllers is the interlock design needed to prevent a glitch or memory fault from activating conflicting phases at once, eg two intersecting approaches getting green simultaneously. That's about as safety-critical as it gets for a piece of everyday infrastructure. Would've liked to see more depth on that, though I imagine the specifics are controller/vendor-specific.
I think that interlock design also goes some way toward mitigating the security risks ASCT systems would otherwise pose, as mentioned in the article. On any decent controller, even the control room shouldn't be able to deliberately trigger conflicting phases.
A typical signal cabinet has a conflict monitor, also called a malfunction management unit, that’s physically distinct from the controller. It supervises the controller outputs and can force the signal to all-way flashing red if green (or yellow or WALK) is shown for conflicting phases or if red or DON’T WALK is missing. More sophisticated units can also detect problems with sequencing or change or clearance interval timing.
Here's a surprising anecdote I've discovered living in South Africa wrt traffic lights.
When they're not working at a busy intersection in my area, the intersection effectively becomes a four way stop. And I've found that as long as everybody follows the rules, traffic actually seems to flow FASTER than when the traffic lights are actually operable.
I've timed this a few times.
I see so many places that could have roundabouts instead of lights. Plus, if the maximum speed inside my town was lowered to 40km/h, we could have shorter yellows. You can never reach the 60km/h limit for more than a few seconds anyway.
Speaking for Johannesburg, we can't have shorter yellows because too many people treat them is "last chance to speed up to make it through before it's red for too long!" and JMPD is beyond useless at law enforcement.
Where I live they've been actively removing traffic lights. One strategy is to turn multi-lane roads into single-lane ones with a lower speed limit, and crossing islands for cyclists and pedestrians. Cars move slower, but more consistently, traffic is better able to self-regulate, so while I haven't timed it, I'm fairly sure traffic is actually moving faster despite driving at lower speeds.
Of course, it helps that infrastructure adjustments over the decades ensures that many people that don't need to be in cars, aren't in cars.
Sounds like you're living in a country where local government actually cares to improve things rather than doing as little work as possible while also self-enriching themselves as much as possible.
There's plenty to criticise at all levels of government here, but overall I indeed am pretty satisfied with my local government. And on the infrastructure level especially - whenever there are roadworks, they're annoying, but I'm always looking forward to what it'll end up as.
I think this would depend on the intersection.
If the lights are at an intersection where a very busy road crosses with a less busy road then turning it into a four way stop just turns it into a traffic jam on the very busy road. I’ve seen this happen during rush hour in the United States multiple times.
When it’s not rush hour though maybe the situation is different? Not sure.
Every time I see an intersection fallback to 4 way stops, traffic slows to a crawl. Roundabouts are the true answer.
I think you mean "robots" ;).
Seriously though, speaking as a South African living basically next to Sandton, there are plenty of traffic lights near to me which cause complete chaos when they are out. They will cause significant delay for the entire working day on certain routes, e.g. anywhere on Winnie Mandela (formerly William Nicol) Drive.
There is however one intersection (Stirling and Balmoral Ave) on the way to my kid's school on a non-major road which definitely works better when its traffic light is out, and this is at any time of day in my experience.
Some traffic lights definitely should rather be mini traffic circles, e.g. on Peter Place by the one office park and had the exact same frustration for the one on Grosvenor Road near to Bryanpark.
As the Johannesburg Road Agency (like all City of Johannesburg Municipal companies) is so incredibly incompetent, our traffic lights are incredibly unreliable, I shudder to think how much it sucks out of our economic output all the people sitting in traffic longer than is needed simply due to an out of order traffic light.
And the local police also don't help with regular roadblocks while at the same time being terrible at law enforcement (yes, you'd think roadblocks are a sign of law enforcement, in practice though they're more for soliciting bribes while screwing up traffic).
The two-adjacent signals causing extra traffic is something I encounter daily in Berkeley -- Ashby / Claremont & Ashby / Domingo. I probably blow an average of 5 minutes a day cause of that double intersection.
To highlight one other point from the video: You want a light to be able to clear the line built up each time. If not, flux in > flux out and that's a recipe for a growing line, which causes a traffic jam.
They are very common all down the SF Peninsula because of the Caltrain tracks. There's California/Carolan all through Burlingame (which has some of the most dangerous train crossings in the country because you can get stuck on the tracks between the lights), and then it follows El Camino on one side while the other one goes from Delaware (San Mateo) to Old County (San Mateo / Belmont / San Carlos) to Alma (Palo Alto) to Central Expressway (Mountain View / Sunnyvale).
The Old County lights at least are staggered so they are almost always green at the same time. The Central Expressway ones, not so much - there've been times I've been stuck for 20 minutes trying to cross the 100 feet from Moffett to Castro in Mountain View, because the light timing never lined up with the train signals.
> there've been times I've been stuck for 20 minutes trying to cross the 100 feet from Moffett to Castro in Mountain View, because the light timing never lined up with the train signals.
They've conveniently solved this by closing the Moffett->Castro side of that intersection entirely. You can still go Castro->Moffett, but they're planning on closing that to eliminate the grade crossing entirely.
Oh, nice. So all traffic is routed over Shoreline and then enters downtown through Villa/Dana? That's a better road for it anyway, with the grade-separated Caltrain & Central Expressway crossings.
Is there still pedestrian access from the northeast side of the Caltrain? I used to live in the Moffett/Middlefield area and being able to walk to downtown was a big draw for that.
> So all traffic is routed over Shoreline and then enters downtown through Villa/Dana?
Yeah, they're planning to put a ramp from the Shoreline bridge over the tracks down to Evelyn to spread out the traffic, but right now people take Villa.
> Is there still pedestrian access from the northeast side of the Caltrain?
Yeah, all the crosswalks are still operational. The long term plan is to put a bike/ped tunnel under Central and to completely close off the Castro/Caltrain side.
Many progressive cities intentionally time their lights for this for two reasons. One is to intentionally limit capacity. Once a road gets past a certain density, you end up with problems that make things astronomically worse (for example: people who "block the box" and cause everything to grind to a halt.)
The second reason: trying to incentivize people onto trains, buses, bikes, foot, etc.
Cambridge, MA does this. The light are purposefully timed to not let you travel through multiple greens on the tertiary roads in particular, less so secondary, etc.
Cambridge also gives a substantial amount of time to pedestrians as part of every cycle- no "beg button", because the city does not consider someone on foot to be less deserving of crossing time - specifically to not have the car "be king". By making it relatively fast to get around on foot, they reduce the incentive to drive.
They also heavily structure the residential neighborhood streets with one-way directions designed to make it very difficult to use the streets people live on as cut-throughs when the main roads jam up because that leads to noise, pollution, and danger to people on foot and bike, particularly because the kind of person to use a neighborhood as a cut-through is likely also driving quickly and aggressively.
Exactly, a road system as a whole has a certain capacity and friction in the system is used intentionally to maintain order. It is a bit like limiting electrical current using resistors in electrical circuits. Sure you could leave them out, but then you will have problems.
> You want a light to be able to clear the line built up each time
Ideally, yes, practically, no. In reality you also have to consider what comes downstream of a traffic light. It doesn't help at all if one traffic light has perfect throughput only to put everything into gridlock in the next node.
That means in most real traffic systems each intersection lane will have to have less then ideal throughput because you don't want to overwhelm the next section, as this could be even worse for the system overall.
If you have some engineering background you can also think about this as impedance matching. If you have a 4 lane road narrowing to 2 lanes you have a sudden impedance increase, leading to flow issues. If you put an intersection inbetween you now have a way to manage that impedance mismatch with signaling times, but you have to both look at the impedance before and after the intersection.
I'm sure AI can figure this out better than a human can. Obvious and empirical, we certainly haven't figured it out or optimized it, with all the engineers that CalTrans has. How often have we been in a four-way controlled intersection and the green is on for the empty side. There's no way that's impedance matching, it's more like Good to go boss, call it a day. There's no incentive to modernize traffic light control because it's public works and there's no capital profit motive for it in the same extent as private. I would not advocate privatizing it either because that will bring different consequences. The hero will be that new young Caltrans engineer who's grown up in the AI generation and will probably be fed up with the legacy technology.
> How often have we been in a four-way controlled intersection and the green is on for the empty side. There's no way that's impedance matching
Who claimed it was tho? We were talking about throughput. If all your intersection knows is time, it can't decide based on traffic. Which is why inductive loops, camera based systems and so on exist, but (1) they are not deployed everywhere and (2) if they are deployed there may still be a time based limit for the case of defective sensors.
Our traffic systems are already pretty well optimized where we are willing to spend money on them. Note however that if you 100% optimize any system for perfect throughput, it has zero slack to deal with unexpected fluctuations in traffic patterns. That is as true for traffic as it is for networks. Throughput is important, but so is comfort, resilience, predictability and cost. All different metrics you have to keep in mind¹ and all of them can suffer when you over-optimize for one.
The view from inside the traffic that we are part of may make that seem inefficient, but seen system wide the main problems usually are not traffic lights, but harder to change structural issues.
¹: or rather you don't have to keep them in mind, since there are people who specialize on just that and are pretty good at it
One thing that I noticed about traffic lights in CA -- there will be like 4-5 cars who are driving on the major road and approaching the traffic light. Then a car arrived from the small road at the intersection. The traffic light will then turn red for cars on the major road, so all 4-5 cars will brake and stop at the light. The small car proceed to turn left into the major road. A few seconds later, the light for the major road turns green again and the 4-5 cars proceed.
I have seen this so often that I sometimes wonder if it'd be more fuel efficient to let the 4-5 cars on the major roadway proceed (the traffic lights have cameras anyway) while letting the one car from the small street wait slightly longer or wait for a fixed amount of time.
I wonder if there's any traffic engineer on HN from California and if so, I'd love to hear an explanation/rationale behind the current approach.
I live in BC near a highway intersection and in my experience they seem to do what you suggest.
I approach from my street and if the highway is empty, almost instant green. Otherwise I have to wait some time until the road clears. During peak hours when the road doesn’t clear, it just seems to go green after a fixed time.
My son and I observed similar behaviour at a puffin crossing on the way to his school, and we’re buildng a model of it using an Arduino Uno with a RCWL-0516.
I'm in the US and I just spent 5 minutes trying to figure out why a bird that can fly needed a special road crossing. I mean, a penguin crossing might make sense in a few places (but not Antarctica because there are no cars or streets there). Where do they have puffins that need to walk across a road?
Duh. Cultural differences in English are amusing.
https://en.wikipedia.org/wiki/Puffin_crossing
I used to live in a south Florida (Miami) suburb and the traffic lights there function like what you suggest too. So after moving back to southern CA, it's something I had to adjust (and the traffic light behavior difference became obvious to me).
Historically, the amount of data available to traffic lights controllers was rather rudimentary, basically a simple presence/occupancy detector covering the area immediately upstream of the stop line and/or some point somewhat (a few seconds of driving time) further upstream of the stop line and/or the whole area in-between. The detector could be implemented via an inductive loop buried within the pavement, or it could be a camera, but with the camera still usually working only as a simple presence detector with no advanced detection capabilities where it could actually intelligently "see" individual vehicles.
With such a setup, the traffic lights controller can't actually see that there's only 4-5 cars approaching on the main road – either they're far away enough that they don't even register on the detector for the main road yet (in which case a vehicle waiting on the crossroad will naturally trigger the phase change without delay), or even if they're already near enough to the intersection to trigger the detector, the traffic lights controller can't actually know that it's "only" 4-5 vehicles and its strategy might hence be that if the main road has had more than x seconds of uninterrupted green time, a demand from the side street will be granted immediately, regardless of traffic conditions.
With a state-of-the-art system it'd be different – with more and better sensors the traffic lights controller could actually track individual vehicles (or platoons of vehicles) as they approach the intersection and try making the kinds of trade-off you mention – but somebody needs to pay for that kind of upgrade. (And I suspect we haven't necessarily reached the point where the price premium for that kind of advanced traffic lights controlled compared to classic traffic actuation is negligible enough for it to be the default at least for all new intersections and equipment renewals, either…)
Reminds me a bit of the MIT study that relates to spacing in densely packed roadways [1]. Whenever I apply the rule (look into my rear view mirror and decide how late to slow down), I feel like a good little molecule in an ideal gas.
[1] https://www.csail.mit.edu/news/improving-traffic-tailgating-...
I highly recommend Traffic Light Doctor on YT, if you're into this sort of thing.
Better not, it would just get me even more pissed off at how crude and incompetent German traffic engineering is. Pretty sure some frustrated worker is making it worse on purpose - you don't reach certain peaks of crappiness accidentally, it takes _work_.
Can't speak to Germany, but one thing I like in the Netherlands is that if you approach an empty intersection the light will automatically turn green for you. Have never seen anything like that in North America.
And the roads themselves are good in NL (huge contrast when I moved to Montreal, where we'd have a metal mesh underneath bridges to catch falling concrete)
According to Claude, NL only has 5500-6000 signaled intersections and of those approximately 900-1450 are of the type you are suggesting (iVRI). The benefit is also higher in NL due to the density and amount of cyclists. iVRI is also not latency sensitive and so installation costs are low as signaling can traverse the regular cellular network.
In the US, we have many more lights due to the road layout (grid). There are more than 3200 signaled intersections in my county in California alone despite being 1/14th of the land area of the NL.
The robot also estimates that there are 300,000 signaled intersections in the US. We honestly don't know how many there are because they are all operated by different agencies.
For US arterial roads iVRI has limited benefit. So the focus in the US has been on V2X development which focuses more on crash avoidance and has much higher installation costs due to latency requirements. In the end there's a lot of low hanging fruit here in the US if signals could just be retimed.
https://transportationops.org/publications/2012-national-tra...
NL has one procurement entity. In the US there is no single coordinating entity to standardize traffic lights. Each state standardizes its own lights and then each municipality handles its own procurement.
I don't know the numbers, but I live in NL and I can't recall the last time I encountered a traffic light that just runs on a timer; as far as I know just about all traffic lights have some awareness of traffic.
Lowering the number of traffic lights in and of itself is a good idea. Overpasses and (turbo)roundabouts, clever right of way, better road hierarchy; there are lots of alternatives that may provide better throughput and more safety for a given intersection.
The Netherlands as a country with 18M inhabitants is best compared to a big city with the surrounding metro area.
It happens in the US but is rare. Mostly it's a road servicing a well connected person or wealthy neighborhood that gets the dwell time reduced to nearly nothing.
There's an annoying one near me at the bottom of a hill where anyone approaching from the sidestreet will ruin the descent on bicycle, even if they were turning right (from a dedicated turn lane) and didn't need the light to change for them at all. Another is a former police station now used as a park facility. Cars entering the parking lot only need to barely brush over the sensor and the light changes instantly for no reason because they never reprogrammed the light when the police left.
> you don't reach certain peaks of crappiness accidentally, it takes _work_.
Have you really never seen what happens when something grows organically without global maintenance? Not saying that this is what happened in Germany, but "it takes work" sounds naive.
It doesn't take work to write a crappy codebase: all you have to do is add code without really caring about the overall architecture.
Or said differently, if you can fix the German traffic engineering, you should apply there because I'm sure they would be happy to have an easy and perfect solution.
What's your issue with traffic in Germany? I know it depends on the city/state, but it always seemed pretty okay to me (though I haven't been driving much in other countries, so I don't have that much experience with "better" systems)
From what I've seen about US traffic, there doesn't seem to be much to be envy of.
came here to say that also...its like 1 of 5 reasons I still use instagram, did not know he was on YT.
> Actuated signal control [...] inductive loop sensors embedded into the road surface
It blows my mind how many people don't realize that's what those circles near the stop bar of an intersection are for, and will then stop 3+ car lengths behind the stop bar, and then can't figure out why the light is never going green.
> two signals closely spaced in a row on a major roadway. If one signal gives a green but the next one doesn’t, cars can back up
This is a major problem at an intersection near me that I used to have to drive through frequently. Two intersections, only about 500 feet between them, and MOST traffic during rush out coming from just one of the directions, yet the lights were often exactly out of sync. The first light would be red while the next one was green. Then the first would go green while the other went red, and traffic would only move about 500 feet then stop for 2 minutes. The backup would last well over a mile.
> The obvious next step in efficiency is coordination of most or all the signals within a traffic network. This is the job of adaptive signal control technologies, or ASCT. [..] These types of systems can dramatically reduce congestion
My cynical ass would not be surprised at all if oil/gas companies were lobbying against ASCT because idling cars are buying more fuel. Wouldn't be too hard to convince people that an ASCT would cost too much to implement while not producing significant traffic benefits.
> This is a major problem at an intersection near me that I used to have to drive through frequently. Two intersections, only about 500 feet between them
In San Francisco (as well as other cities I've lived in) they put police in the middle of intersections during rush hour to guide traffic (i.e., stop cars before they drive into an intersection that they'll get stuck in the middle of). Seems woefully inefficient
When traffic is really heavy humans are better than machines at getting traffic through. However they cost a lot of money and so are only rarely worth the cost.
It might be more about drivers respecting the signals than about the efficiency at which the signals are handed out. Plenty of people will try to squeeze into a yellow light even if they might get stuck on the intersection if the road is backed up but they are less likely to do so with a police officer watching them.
There is that, but also the police can see that the road will backup and stop traffic before that happens. They let someone who is going to a non-backed up road go instead. They also can see a road is backing up and give that high priority if there is a place for the cars to go.
The traffic cops greatly improve throughput.
Imagine how much gas would be saved if the city spent a little effort on the traffic lights.
How much gas would be saved by turning half of each 4-lane stroad into a bike lane! :)
There are many bike lanes where I live, all installed in the last few years.
The bike traffic remains 1% of the car traffic, and 0% when it's cold/rainy.
Oh man, so much to be said about those two short, crass sentences... x)
You could also save some electricity by turning off your computer and never turning it back on.
It's not really saving gas if your alternative doesn't achieve even remotely the same thing.
ASCT is standard practice (and has been standard practice) on most junctions in most towns and cities in the UK for over 20 years.
Curious...in the UK, is the implementation of something like that done by government employees?
In the USA, a significant amount of tax-funded infrastructure is actually built out by contractors, which means there's profit going to a corporation, and there's often a cynical idea that the contracts go out to whoever will send a kickback in the form of a campaign contribution to whoever makes the decision on which contractor to use.
The local councils (local Authority) usually get external companies to design the systems, but there are standard, off the shelf solutions that are specified to be used. These systems range from time synced junctions (with Vehicle attenuation) up to full Urban Traffic Control systems, the protocols used are mostly standard (UTMC), so the local Authority just needs to say what they need. For a UTC system it used to be that the council would run the instation, but with cloud computing, that's mostly run for them now as a hosted system. Usually this is all controlled by the standard local council procurement rules, and run by council employees not elected officials. The elected officials can say a scheme is needed and approve costs, but not who does it.
UK council election spending limit is £960, so not a lot of scope for big "contributions" as bribes. https://www.electoralcommission.org.uk/guidance-candidates-a...
That means all the bribery has to be firmly under the table instead, rather than legalized.
If I had a nickle for every time I’ve had to get out of my car and walk up to the person in front of me and explain that they need to pull forward for the light to change - I’d have two nickels, yadda yadda yadda.
> My cynical ass would not be surprised at all if oil/gas companies were lobbying against ASCT because idling cars are buying more fuel. Wouldn't be too hard to convince people that an ASCT would cost too much to implement while not producing significant traffic benefits.
I don't think you need a vast conspiracy to point out that connecting traffic signals costs more (fancier signal equipment, running cable, maintaining the cables, etc) and the benefits may be subtle, hard to predict, and maybe even hard to measure.
Additionally, you have a lot of people that would prefer to slow traffic. Depending on local culture, investing in traffic control can be difficult (although upgrading traffic signal systems may be better able to accomodate priority for transit and bicycle detection)
Back when I rode I had to add a giant hunk of iron to the bottom of my motorcycle so these fuckin things could see me. Sometimes that still isn't enough and after a few minutes of shimmying back and forth over it I'd just run the red
Yup. It becomes crystal clear that nobody in authority in roadworks & traffic drives a motorcycle.
"that's bad, peasants shouldn't do that, so we won't support it to make it suck"
> M y cynical ass would not be surprised at all if oil/gas companies were lobbying against ASCT because idling cars are buying more fuel
This is a bizarre conspiracy theory that you just invented. Stop making up things to get angry about.
I didn't say I think it's happening, just that it wouldn't surprise me if it was.
There's a major arterial near my house. One day, the power went out in the area, and the traffic lights went dead. I discovered to my amusement that throughput on the arterial and its crossings increased dramatically, as drivers simply cooperated with each other.
There are already cameras on top of all the lights. How hard can it be to hook them up to AI that is instructed to maximize throughput? The current system will block 3 directions while having a green light on the 4th which has no traffic.
I once complained to a friend about this, and he told me that the traffic engineers were experts and I was lying. The next day I was driving on that road, and got a red light. You could see on down the distance 3 greens. There was no other traffic, and no cross traffic. So I sent him a photo. He conceded :-)
I guess the main reason traffic lights exist is to avoid incidents, not necessarily to maximize throughput. Maximizing throughput is just a nice no have, and so no one bothers. Just a guess though, I've no idea what I'm talking about.
> How hard can it be to hook them up to AI that is instructed to maximize throughput? The current system will block 3 directions while having a green light on the 4th which has no traffic.
You don't need AI for that, you just need the system configured properly. Lights near my parents' house have been running cycles adapted to actual traffic for at least two decades, probably three... although using inductive loops in pavement rather than cameras.
There are reasons you might want a short green every so often even with no detected traffic... it would help manage worst case situations for a stuck open detector, etc. But those wasted greens shouldn't be long enough to notice. You might also have situations where locally suboptimal behaviors improves performance or safety elsewhere and that may lead to a better overall system results. I'm not claiming this is the situation in your scenario, but it can explain some negative experiences.
Red lights also regulate speed, although I don't know if they are intentionally de-optimized from green for this reason.
I often hear that the lights are timed. I've never encountered a street where they were timed.
I've certainly seen it in places... There's routes I drove where if you had a green and you keep within narrow speed ranges, you get greens, and if you go at the inbetween speeds, you get reds. Some of those might not be 100% consistent if something interrupts the regular cycle like a pedestrian crossing or an emergency vehicle.
Otoh, Milwaukee circa 2003 had all the lights on a schedule. Every intersection made the same changes every day. Super frustrating when I was consistently slow to get out of the house for a scheduled pickup and missed the light everytime.
> There are already cameras on top of all the lights.
Those are infrared sensors that pick up the heat from car engines. They've had to be modified to pick up electric cars.
> How hard can it be to hook them up to AI that is instructed to maximize throughput?
The equipment cabinet at the intersection has been engineered to prevent all sorts of fatal things that happened in the past. Such as one set of relays being stuck so that one direction always gets a green light while the other direction gets red/yellow/green. They're designed so that can never happen again (when "broken", you'll see blinking red in all directions).
The controllers need to be standardized so that you don't need experts to be able to diagnose & repair them. They also need to be certified. It is not possible to certify an expert system (or as they're now called "AI") because it is not possible to use formal methods to prove correctness.
> The current system will block 3 directions while having a green light on the 4th which has no traffic.
That specific intersection is set on a timer. For a single, 2-lane each way, non-complicated intersection, it can cost $100k for the lights, poles, sensors and equipment cabinet. Every wire is underground in pipes so that the expansion of concrete in weather won't stretch/break the wires.
> as drivers simply cooperated with each other.
That's something that most people learn in kindergarten: "share with others" and "take turns".
Where I live (fly-over country), when the power is out, traffic backs up significantly.
Disclaimer: I used to work for my state's combination DMV & highway department.
Actual "Expert systems" could in principle get certified because they have explicable behaviour. The juice isn't worth the squeeze but it could be done. However the LLMs do not, we don't really know why this does anything even vaguely useful and we can't say if it might fail, or how we'd know. Useless.
> Those are infrared sensors that pick up the heat from car engines. They've had to be modified to pick up electric cars.
Do they pick up ICE motorcycles ? Electric motorcycles ?
I'm sorry, but that all sounds like excuses. None of it looks like it should impede using AI-developed algorithms.
Heck, an AI isn't even needed. A simple cost function could be easily developed, where each car accrues priority as it waits, and the lights go green on the ones with the highest priority.
I used to work at a traffic signal controller company. We were under strict orders not to use AI. We did anyway, in a simulation, and let it optimize over the weekend. When we got back it had blown all of our previous attempts out of the water. We huddled around my coworker's workstation eager to see its masterful new pattern. It just made one phase red all the time and one phase green all the time, effectively closing one road. The throughput on the other road was through the roof though, since its light was always green. We did not present these results to the boss.
A parameter that gives a max wait time for cross traffic is needed.
A lot of lights exist not to add throughput, but to replace 2-way stops where less performant traffic (so like idiots, grandmas and heavy trucks) would have problems getting in, say fuggit (or get honked at, get flustered) and cause a near miss at least.
Yeah, my city traffic engineer is an ass too. There was an intersection I went through every time I left my old house. Outside of rush hour, it functioned much better as a four-way stop than a signalled intersection. I pointed this out and he said “that is inappropriate for two arterials”. Um, I live there. You don’t.
I always thought that traffic signals should be trying to minimize squared anger, where anger increases linearly with time spent waiting at intersection.
one thing that drives me nuts is a left turn arrow that isn't long enough to clear all the cars waiting in the left turn lane. So often, it would only need another 5-10 seconds but it seems to have a limit that it can't exceed. This leads to frustrated drivers trying to squeeze through on the yellow light or even the red.
Also red left turn signals should not be a thing. If there's a gap in the oncoming traffic you should be allowed to turn left across it as long as the straight-ahead traffic has a green light.
> red left turn signals should not be a thing
Where I live (in the PNW) they mostly are not a thing any more. The only ones remaining are there because the combination of sight line and traffic speed makes them too dangerous to turn into flashing yellow. Not sure if that has spread to other regions, but I would guess it is heading towards being universal pretty quickly.
Preach!
The only possible second-or-third order effect of red cross-traffic arrows is to decrease the downstream traffic on the cross road. Mostly, the places where I encounter them have a low traffic cross road. IMHO, in those situations, red cross-traffic arrows are simply a failed "traffic engineering fad".
(Edited to fix a typo and generalize "red left-arrow" to "red cross-traffic arrow" to account for left-side-of-the-road driving systems.)
I'll grant that it might be safer for pedestrians, as then they only have to watch for right-turning traffic and not people turning left from the opposite side of the road. There are a lot of intersections that rarely see pedestrian traffic though.
Fair point.
I live in a small city in rural area (Nevada City/Nevada County, ca).
Traffic lights here are unbearable. The situation, as I understand it, is that there's tradeoff between through-put and latency. Basically, if you make each cycle of a light really long, like 1-2 minutes, then how many cars get through, can be maximize. Sounds good but such optimizations drive the average driver f---kin nut. I don't think that cost should be ignored.
>As sensors become more ubiquitous and computing power increases, traffic management may slowly but surely be relegated from civil engineers to software developers and data scientists. But, that also means that ASCT systems may be more vulnerable to security threats, a scary thought if they’re controlling the signals for an entire city.
I feel like software engineers would write more secure software than civil engineers. It would be the opposite. I'm also not scared that much of someone controlling traffic lights. It's already possible using emergency lights.
ASTC systems do not "dramatically reduce congestion." They result in a small (probably single digits) increase in traffic flow at best, which is a rounding error. God, I'm sick of this dude's flyover videos and him being treated like some genius.
Numerous cities don't bother with ASTC systems because they a)don't do very much yet cost a lot of money in equipment and staffing, and b)just further incentivize low occupant vehicle traffic, which is just about the lowest priority in most cities these days because that in turn creates more traffic. If there was one overarching tenet to traffic engineering and urban transportation planning, it's that you cannot solve traffic by building more roads. It doesn't work. It has never worked.
Traffic is something 99% of the population thinks they understand because they sit in it, see it, etc. and probably 95% don't have the foggiest idea how it actually works, and merely have a severely uneducated and highly biased personal opinion. And boy howdy, do they hate bike lanes and bus lanes.
Adding (or removing) a lane does not even remotely have a direct correlation to maximum traffic flow. If you have a three lane road and you make one lane a bus or bike or bus-and-bike lane, you do not lose 1/3rd the traffic flow capacity. It's dramatically less than that.
By making bus transit faster (where each bus holds ~60 people...) and biking safer, not only do you actually reduce traffic, but you also provide emergency vehicles with a faster route through traffic.
In Paris more people travel by bicycle than car. That was a direct result of Paris heavily restricting motor vehicle traffic through the center.
Every person on a bicycle is one less person causing noise, pollution, congestion, wear to the road, danger to others, and using (at least) one less parking space (because you don't just need a place to put the car where it is kept, you also need space for where it is going.)
Simcity designers initially based Simcity off actual real-world stats and planning figures. They had to throw out the figures for parking and road capacity because otherwise the game would have looked like nothing but roads and parking lots.
> Adding (or removing) a lane does not even remotely have a direct correlation to maximum traffic flow.
Of course it does. What an obviously stupid thing to say. You think a 4 lane motorway doesn't allow more traffic flow than a single lane country road?
What I find most interesting about the computer side of traffic signal controllers is the interlock design needed to prevent a glitch or memory fault from activating conflicting phases at once, eg two intersecting approaches getting green simultaneously. That's about as safety-critical as it gets for a piece of everyday infrastructure. Would've liked to see more depth on that, though I imagine the specifics are controller/vendor-specific.
I think that interlock design also goes some way toward mitigating the security risks ASCT systems would otherwise pose, as mentioned in the article. On any decent controller, even the control room shouldn't be able to deliberately trigger conflicting phases.
A typical signal cabinet has a conflict monitor, also called a malfunction management unit, that’s physically distinct from the controller. It supervises the controller outputs and can force the signal to all-way flashing red if green (or yellow or WALK) is shown for conflicting phases or if red or DON’T WALK is missing. More sophisticated units can also detect problems with sequencing or change or clearance interval timing.