In the end the availability comes down to fleet size. car2go worked best here when they blanketed Seattle with Smart Cars, the fleet peaked around 750 and they

In the end the availability comes down to fleet size. car2go worked best here when they blanketed Seattle with Smart Cars, the fleet peaked around 750 and they were easy to find. After they switched to Mercedes exclusively the fleet was smaller and it became harder (though not impossible) to find them close by. My guess is that 2,500 cars would be enough to make them feel ubiquitous. A small fleet of autonomous cars won't mean it's likely one will be available to pick you up, and nobody has figured out how to deploy & maintain them at scale yet (I think Waymo in Phoenix is only running around a hundred vehicles).