Though I’ve heard people treat it differently in the US
It makes less sense in an urban environment with 5 or more lanes in your direction. Vehicles will be traveling at varying speeds in all lanes, ideally with a monotonic gradient, but it just doesn't happen, and it's unlikely to.
In California, large trucks generally have a lower speed limit (however many trucks are not speed governed and do exceed the truck limit and sometimes the car limit) and lane restrictions on large highways. Waymo may do well if it tends toward staying in the lanes where trucks are allowed as those tend to flow closer to posted car speed limits. But sometimes there's left exits, and sometimes traffic flow is really poor on many right lanes because of upcoming exits. And during commute time, I think the HOV lane would be preferred; taxis are generally eligible for the HOV lane even when only the driver is present, but I don't know about self-driving with a single or no occupant.
(also it’s kind of amazing that 5 parallel lanes is considered normal in the US… I think the most I’ve ever personally seen in the UK is 4 and that’s only on very major routes, and we don’t have any exits on the wrong side of the motorway)