Speed doesn't matter at all in city driving on regular roads. Going from 35mph to 25mph doesn't materially affect the trip time.

Think about SF, its size is (famously) around 7 by 7 miles. So it'd take 12 minutes to cross (as the bird flies) from one side to another at 35 mph and 17 minutes at 25mph. Which is completely unrealistic, because real travel times are dominated by traffic lights and congestion.

This calculation changes only when we're talking about long-distance travel on freeways. But honestly, I expect that fast long-distance trains with seamless transfer to self-driving taxis would be a better idea.

> Going from 35mph to 25mph

...dramatically reduces likelihood and consequences of a crash