This isn't the way it works. If a car says it can do "Level 4 on a sunny day" it means when you sit in the car and engage the autopilot (and it says it's safe to engage), then no human intervention will not be required during the course of the trip. If conditions change, the car will be parked without human assistance and wait for help (what happens next is outside of the scope). You could be sitting in the back seat, or your kids could be in the car alone on their way to school.

"Level 4 on a sunny day on some pre-certified highways" is ok. "Level 4 in San Francisco traffic" is also ok, and much harder. "Level 4 unless it starts raining and we'll deteriorate to Level 3" is Level 3, not 4.

This is the definition of autonomy levels from SAE, and they're pretty strictly defined.