Waymo (at this time) is an alternative to taxis and ride hailing services. I've lived in SF for 30+ years and used all modes of transit here. Some of my most frightening moments on the road have been in taxis with drivers who are reckless, in badly maintained vehicles, sometimes smelling of booze. There are certainly other ways that taxis could have been improved, but given the way things have evolved (or devolved with taxis), I feel much safer in a Waymo.
Any comparison of Waymo's safety should be done against taxis/Uber/Lyft/etc. A comparison with the general driving public could also be interesting, or other commercial drivers, but those are not the most relevant cohorts. I don't know the numbers, but I wouldn't be surprised if taxis/Uber/Lyft are worse per mile than general drivers since they are likely under more stress, and often work for long hours. A Waymo is no less safe at 4am, but a Lyft driver who's been up all night is a lot less safe. I would also guess that they are less likely than the general (auto) driving population to own their vehicle. Depending on who owns a vehicle, how long they've been driving (years), there's going to be a lot of interesting correlations.
Any comparison of Waymo's safety should be done against taxis/Uber/Lyft/etc. A comparison with the general driving public could also be interesting, or other commercial drivers, but those are not the most relevant cohorts. I don't know the numbers, but I wouldn't be surprised if taxis/Uber/Lyft are worse per mile than general drivers since they are likely under more stress, and often work for long hours. A Waymo is no less safe at 4am, but a Lyft driver who's been up all night is a lot less safe. I would also guess that they are less likely than the general (auto) driving population to own their vehicle. Depending on who owns a vehicle, how long they've been driving (years), there's going to be a lot of interesting correlations.