I see some cars disappearing

edit: actually if it hits an end of a road, it spawns to a lane next to it either goes opposite direction or turns (referencing first gif)

Wonder if they could have considered ensuring no cars stack on top of each other

There are some rules where in their collision detection they basically don't check; for example cars going east will never intersect with cars going south so just drive through them. I'm not sure if this was an optimisation to just speed up collision detection by checking fewer cases or they were trying to prevent too many traffic jams by having better collision detection. Probably a bit of both :)