My homeward journey often took me north on the 405 freeway, where it passes under an overpass of the northbound 5 freeway. The 405 north always slows just before this junction, since there is a turn in the freeway and a merge right afterward. The overpass creates a four-lane wide tunnel, and there is a phenomenon that occurs there that I haven't witnessed elsewhere on LA's freeways. People honk, but only under the shadow of that overpass. Nobody honks before or after unless there's an actual or almost a collision. LA drivers don't honk very often, they just cut each other off and keep moving. The 'rules' of this emergent 'game' are that you can only honk while you are in the shadow of the overpass. Once you're in the sun again on the other side, no more honking.