I’m not sure I understand the situation. Why would a slow street somewhere in the vicinity force a car to detour and U-turn on a cul de sac? Way I makes it sound like human drivers would have to do the same, which sounds unlikely.
https://www.google.com/maps/place/Lake+St+%26+15th+Ave,+San+...
So, the self driving car thinks it can go down that road, sees the "nope" and then has to go make a U turn somewhere.
However, this isn't a permeant feature, nor is there communication between vehicles about transient issues. Furthermore, it looks to google maps to be an optimal route - there's very little traffic on it. So the car goes there, discovers that it can't go that way and then needs to reroute. The classic "make a U turn at your earliest opportunity" type navigation assistant then sends it to this dead end where it can legally make a multi point turn.
Also Google Maps seems to have the slow street marked. Do Waymo cars not know about that? If you entered the desired route into Google Maps, what way would it take you?
A car going down 15th in the 100 block is either local traffic to something 1xx 15th, or either block on Lake; or is going to be doing a U turn to get back to California.
Playing with Google Maps, it seems smart enough to not route me on Lake. So I guess Waymo's route making software doesn't use all the information that Google Maps has, such as slow streets.
It is super odd that Google maps gets this right and Waymo cars don’t. You’d think they have time-sensitive map info as part of their routing.