I think the top purpose is safety and from there it’s an attempt at optimization. Or perhaps those priorities are flipped. But if you consider Europe which largely favors traffic circles over lights, that’s probably the optimum for keeping cars moving. If I were a selfish car driver in the US, I would want probably ~70% of the traffic lights at all the low-flow intersections to be replaced with traffic circles.

I suppose it won’t be long before this discussion becomes moot. People on their tablets in self-driving cars won’t care whether the car is moving or not.