True, but believe it or not it is incredibly difficult to get right.
I'm on my local council and we recently did some prep work to look into adding "AI" to the towns traffic lights.
Here is the problem; you have to do a significant portion of the lights - or it actually gets worse. A stupid amount of planning goes into light sequencing (at least it does here....) on a macro-scale - so all of the towns lights are pretty much synced to optimize traffic flow as much as possible.
Imagine doing that on the fly for the entire town.
What ''has'' been suggested, and looks good, is a sort of hybrid approach - where traffic levels are monitored and a number of different optimized sequences used to clear traffic jams as appropriate. Even this is a pain because it is essentially the same as replacing the towns system three or four times over :)
And we are lucky in having a medium sized town with large areas of uninhabited farmland (read little traffic) around it.
Not that it isn't a good idea - but I don't think it is a very simple option.