Protected left turns don’t work well without insanely wide roads. There is not room for protected left turn lanes in most of sf, and too much traffic to do one direction at a time signals.
I've not driven in San Francisco. Are cars allowed to sit and block an entire lane until they can turn left? That is how things worked in the rural town I grew up in, but I can't imagine it working in a city. All the streets in the city I live in now which are too narrow for a turn lane are either one-way (thus have no need for a protected left) or they prohibit left turns.
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