It takes time, and it won't need to be perfect for people to take risks. Usually it means they are good enough and make them a lot of money.Following this logic then level 5 full autonomous driving isn't possible if software and hardware can't come up with every possible scenario.
Horses can go through a lot of places that cars couldn't but eventually human move on to cars despite not being perfect, and roads and traffic rules change to make them good enough or better. Eventually roads will probably upgrade to dedicated self driving only lane that would change direction between traffic congestion and when arranged correctly, will have all 4 directions heading into a red light for human driver time slot without crashing into each other. We are not there yet, but one day we will.