We have one here as part of a CMU research deployment: https://www.transportation.gov/utc/surtrac-people-upgrading-...

> The system applies artificial intelligence to traffic signals equipped with cameras or radars adapting in realtime to dynamic traffic patterns of complex urban grids, experienced in neighborhoods like East Liberty in the City of Pittsburgh

Now, that said, I have serious issues with that system: It seemed heavily biased to vehicle throughput over pedestrians, and it's not at all clear that it was making the right long-term choice as far as the incentives it created. But it _was_ cameras watching traffic to influence signaling.

https://www.transportation.gov/utc/surtrac-people-upgrading-...

https://en.wikipedia.org/wiki/Scalable_Urban_Traffic_Control

I see them everywhere in Metro Atlanta. You can tell because there’s what looks like a little camera above each direction facing traffic light.