A significant portion of US highways and backroads are uncovered by cell signal. I suppose a self driving car would have starlink these days.

We once had no gas stations, now we have 150,000 (in the US). If the commercial need is there, building out connectivity is an unlikely impediment. Starlink et al. can solve this everywhere except when there's severe weather, a problem Waymo shares, which is starting to make me think the Upper Midwest might be waiting a very long time for self-driving cars.