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.

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…)

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.

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.

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).

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.

> 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.

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.

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.

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

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.

> 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

> 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)

ASCT is standard practice (and has been standard practice) on most junctions in most towns and cities in the UK for over 20 years.

> 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.

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_.

came here to say that also...its like 1 of 5 reasons I still use instagram, did not know he was on YT.

> 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 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.

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.

> 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.

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.

> 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?

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.

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.