Google’s autonomous vehicle company Waymo has won regulatory approval to start testing SAE Level 4 driving without a human backup in California, despite running into teething troubles during similar trials in neighboring Arizona. Waymo gained the go-ahead for trials in Arizona sooner because the state is less populous with many small roads almost deserted and even major highways well suited to testing of autonomous driving with long open stretches and usually excellent visibility. But when the tests encroached on the suburbs of the state’s one major city, Phoenix, several deficiencies came to light. These mostly concerned maneuvers such as turning left across the face of oncoming traffic, changing lanes under congestion and navigating around clusters of pedestrians. In such cases,…