To communicate with all the other traffic lights and sensors at the other intersections on the road to optimize traffic flow.

Yeah, I still think that's overkill, simply because the bulk of the computation is done on a remote server anyways. All you really need on the frontend is a TCP/IP stack to send telemetry and receive commands.

If the connection is lost, the exchange can just fallback to "naive" mode.

I guess using off-the-shelf mass market hardware combined with a software stack anyone can design, setup, and implement is way easier and cheaper than a customized solution.

Consider the overhead of maintaining two entirely separate software stacks, with different libraries and controllers then? And the ongoing costs of discovering your "minimal" hardware can't accomodate a future improvement, compared to just using general compute at a marginal upfront cost, and then having everything else be familiar?

Such thing does exist? I thought traffict light only time-based on no sensor involved.

Depends on the area but yeah many intersections use sensors (cameras, sometimes under the road pressure sensors, etc) to make anywhere from subtle to extreme changes based on traffic patterns. The under the road pressure sensor has been around for decades.

When I was a kid there was one light that, when you drove over the pressure sensor, it wouldn't really do much. But if you backed up and drove over it again it must have registered an additional car coming through and the light would almost immediately go through its light cycle to change. It was really interesting to see!

Nowadays I think it's mostly cameras? We have a light near my home and the left signal will literally never trigger unless someone is in one of the left lanes.

It's not a pressure sensor, but an induction loop. Basically, there is a coil placed on the road that has a small AC current passed through it. When a car (metal) sits on top of the coil, the two "coils" couple, changing the overall inductance. A simple sensor can detect this change.

The current is even able to pass through the tires?

No, the current passes through the coil, and the coil has no physical contact with the vehicle.

Look up inductive coupling. The basic idea is that a changing (AC) current in a conductor generates a changing magnetic field (Ampere's law). This changing magnetic field then induces a voltage in the second conductor (Faraday's law). This is the principle behind how transformers work.

As far as I understand, it's just electromagnetic waves. No current passing through to the car, but the coil can "register" a change in its magnetic field and can determine that it's a car and how fast it goes

Can confirm. Also interesting to note that motorcycles often have trouble triggering these sensors (a common trick is to stick a heavy duty magnet underneath).

Really interesting! Thanks for the correction!

As a sibling comment noted, it's not a pressure sensor [1] but an induction loop.

The Wikipedia article https://en.wikipedia.org/wiki/Induction_loop#Vehicle_detecti... has fairly extensive details on modern implementation.

[1] These do exist for weight-in-motion systems, however.

An OS has a kernel. TRON [1] equally fits your description. Which is IIRC what traditionally runs on traffic lights.

[1] https://en.wikipedia.org/wiki/TRON_project