>> The problem is that the system you're proposing introduces an extra step before turning. That is, yield to a bus, then to a cyclist, then to pedestrians.
>> The more steps there are, the more likely one will make a mistake and fail to yield because they failed to account for one of the steps necessary to successfully make a turn.
> that's actually a traffic calming technique, to make car drivers more attentive and more purposeful/communicative, rather than driving on (human or machine) auto-pilot all the time. more obvious collision dangers make car drivers more mindful
I don't really know if this assumption holds. Collisions are more common complex intersections versus simple ones. For example, one is more likely to get into a collision when making a left turn from a side road because they have to check for pedestrians approaching from the left, pedestrians approaching from the right traffic approaching from the left, traffic approaching from the right, and possibly traffic entering the roadway directly across from them.
If you contrast that with a roundabout, when entering, one has to check for pedestrians approaching from the left, pedestrians approaching from the right, and traffic approaching from the left. Because there are fewer things to check for, the chance of getting into a collision is reduced.
The other part of it is when exiting the intersection. After one has started turning, one needs to check for any pedestrians who may be crossing before completing their turn, so that's another step that the left turning driver has to account for. With a roundabout, that check is postponed and actually can be thought of as a separate check once they get to the exit of the roundabout (checking for pedestrians). You could get a similar spacing between checks if, instead of making a left turn, make a right turn and then a u-turn.
In the case of the right turn crossing muliple lanes of traffic, the driver not only has to check for more things, but they don't have the time spacing to re-orient themselves to get ready for the next check. That increases the probability that the driver may fail to check before proceeding.