To many drivers round here it appears to mean "let 3 cars through, then everyone else has to stop"
Honestly, this is what happens. Three drivers who actually have a clue about traffic signals go through. Then the 4th driver gets overloaded with information and cant understand why all these cars have gone against a red light. AAAAAH!!!! FFS. Occasionally the drivers in the left lane, turning left, actually move off, because they see everyone else in the other 2 lanes moving! Very worrying, since this signal occurs when peds are crossing the road to the left. They must think the computer that controls the lights has crashed or something.