Head of Line
Virtual Output Queue
in a single lane, the first car is left turning, even in a green light, all other cars, no matter turn right, or go straight, must wait for the left-turn car. this is called HOL
if we have a second extra lane for left turn only, even left turn car is still wait, the straight and right trun traffic is not blocked.
the best scenario is for each direction we have a lane.
it is too resource consume solution..
so the last solution is have dynamic resource for Lane!
which is called VoQ