I could be wrong, but it seems like most intersections in LA are still timer-based. As a consequence, long lines of cars may be stuck waiting at an intersection while there is no cross traffic.

There has to be a way to not only better synchronize lights, but optimize them as well, by means of traffic-awareness and algorithms. I don't think this would require much construction; instalation of new sensors maybe, but most of the work would be software-based...