In such a case, they might not be considered legally at fault, but they would still be, in practical terms, a significant cause of the crash.
A driver -- legally, logically, practically -- should always maintain a safe following distance from the vehicle in front of them so that they can stop safely. It doesn't matter if the vehicle in front of them suddenly slams on the brakes because a child or plastic bag jumped in front of them, because they suddenly realized they need to make a left turn, or mixed up the pedals.
Sure, the current system won't make those bad drivers pay up for that behavior, but dumping a bunch of them onto the roads is a net negative overall.
But if there's an existing system and culture of driving that has certain expectations built up over a century+ of collective behavior, and then you drop into that culture a new element that systematically brakes more suddenly and unexpectedly, regardless of whether the human drivers were doing the right thing beforehand, it is both reasonable and accurate to say that the introduction of the self-driving cars contributed significantly to the increase in crashes.
If they become ubiquitous, and retain this pattern, then over time, drivers will learn it. But it will take years—probably decades—and cause increased crashes due to this pattern during that time (assuming, again, that the pattern itself remains).
Waymo’s crashes that I’ve looked at have just been fairly typical someone else is blatantly at fault no unusual behavior on Waymo’s part. So while it’s possible such a thing exists it’s not common enough to matter here.
While tailgating is tiny slice of fatal collisions -- something like 2% -- it accounts for like 1/3 of non-fatal collisions.
We're already basically at Peak Tailgating Collisions, without self-driving cars, and I'd happily put a tenner on rear-end collisions going down with self-driving cars because, even if they stop suddenly more often, at least they don't tailgate.
And it's entirely self-inflicted! You can just not tailgate; it's not even like tailgating let's you go faster, it just lets you go the exact same speed 200 feet down the road.
Preach.
I was coming home a few evenings ago in the dark, and both I and my passenger were getting continually aggravated by the car that was following too close behind us, with their headlights reflecting in the wing mirrors alternately into each of our faces.
They kept that up for at least 10 miles.