Around here (and everywhere else I've been in the US), around 11pm-6am all lights at non-major intersections flash red or yellow (Major intersections function as normal). Flashing yellow tends to be treated as a green light, as the other directions always have a flashing red light that is to be treated as a stop sign. This has unfortunately caused quite a few accidents for me in single player before I realized it, and some real close calls because of habits in MP, as the game's quite a bit off when it comes to realism with the layouts and whatnot
Neat article is neat
Great guide, though!