10 percentage points, 25% relative improvement (40% non-5 stars to 30%), seems quite good to me.
Although I wonder if seasonality is important here - obviously Phoenix isn't Minnesota but could driving conditions have been worse in Q1 compared to this summer, from the perspective of a self-driving car?
Definitely could be a factor. Other drivers might also be more used to seeing them on the road, which could have a positive impact in some way. I think the overall trend is probably pretty strong at that level of improvement, though.
Although I wonder if seasonality is important here - obviously Phoenix isn't Minnesota but could driving conditions have been worse in Q1 compared to this summer, from the perspective of a self-driving car?