Nor are they easy to redesign. Pittsburgh, Boston, Paris, etc. are generally designed in ways that everyone knows are suboptimal, but the alternative is a catastrophic shutdown in the heart of the city.

It is sometimes amazing how stupid traffic light systems are. One is giving left turning traffic and straight traffic going in the opposite direction green at the same time. That can be solved easily by making sure that all traffic that gets a green light can actually proceed across the intersection. This may need to vary with traffic density, but that's just a technical problem.

The bigger one is to make sure that the next traffic signal down the road is also green. To avoid traffic piling up on an intersection because it has nowhere to go. Of course, this should also depends on the amount of traffic.

Any city can in theory build systems where traffic that wants to go to empty roads gets more green and any traffic that wants to go to full roads gets less green.

You don't think traffic engineers have thought of that? Like, "it's easy to fix this complicated systems problem with no downsides, these idiots just haven't listened to me yet."

https://xkcd.com/793/

I'm fairly sure Boston has intentionally staggered lights to ensure that drivers don't get successive greens in some areas. I would also bet good money that the alternative is some kind of horrific gridlock from emptying side streets too slowly.

Honestly, I'm amazed urban traffic is as good as it is, since the core problems are usually irreducible. (i.e. more people want to go to a place than fit there.) A quick look at gridlock in cities where traffic signals aren't carefully planned and widely respected shows just how bad things can get.

(Suburban traffic is another story, but that mostly seems to be about overbuilt roads with no actual planning at all. My hometown has a couple of intersections that literally don't function - you can get caught at a permanent red light.)

They are a combination of timers and sensors. And yes, we know all about this. Your assumption is correct. Doing this allows traffic to move with greater throughput overall. If it wasn't done, heavier trafficked thoroughfares would have long periods where they were the only priority.

Err... I modeled traffic.

The possible solution would be roundabouts and yield signs, but that would be expensive, require redesign, and we humans pretty much suck at roundabouts.

Intersections are generally a problem because they are constrained by a host of other factors. Complex problem + limited budget generally result in poor implementations. However, in a large enough context you can remove buildings and move roads etc.

So, these things are very much fixable given sufficient priority and resources.

> However, in a large enough context you can remove buildings and move roads etc.

Pittsburgh isn't flat, many times it is not "move this road." It's bore through this mountain, build this bridge, fix the drainage issues around this creek, etc. and fixing intersections almost always leads to more issues downstream.