Ars Technica writes that at first the taxis will have a Waymo employee in them so they can hit the "pull over" button in the event of an emergency.

This puts Waymo ahead of competitor Uber, which is still refining its autonomous approach for commercial trucks, Otto. Uber's consumer-facing autonomous ride service had a small number of self-driving cars in Pennsylvania, but safety concerns (among other, more political reasons) have slowed progress. That's not to mention the IP-theft lawsuit that's been brewing between Waymo and Uber, either.