London also has a subway system that looks like this:
So, yeah, having less freeways can work for them.
Preventing more autos from entering the city and requiring those people to take public transit would implode the entire system as it stands right now.
And I'm sure that London's subway/ rail system has an average speed much higher than 15 mph.
I have a car and sometimes prefer driving but I will be the first to say that I would much prefer that there be a way to get around SF *quickly* by rail or subway than driving. Driving in the city is maddening.