The way traffic lights operate is archaic. Most are on a timer and operate disconnected from the rest of the system. This can be solved using lights that can better detect traffic flow and communicate with lights further up the road. A smart road system. Say you've got 20 cars coming up the road and nobody coming the other way. The light sees this, changes green, and then tells the next light up what's coming. So that light can then use this information to make an intelligent decision whether to stop traffic or keep it moving.
I came up with a basic design for how I could implement this but I have no idea how to make it function.