Captain
Final Approach
Drivers that wait for three or four car lengths to develop before moving on a green light.
That's why only two cars get through at a time, dimwit, keep it tight, get through the intersection, THEN open the gap.
People who don't get physics.
I think that's the main contributor to city traffic. When someone does that (and a good majority do), only 3 cars can get through the light when at least 7 should have. 