That’s not how the math works. At a 0.00034% chance of an anomaly every mile, you have a 50% chance of an anomaly every 200,000 miles. (1-0.0000034)^200,000. Humans go 500,000 miles between crashes. Of course an anomaly doesn’t necessarily mean a crash, but if you don’t require the human operator to be paying attention all the time, it could well lead to a crash with a high probability. Indeed, because a anomaly would likely confuse a whole bunch of cars on the road at the same time, it could well lead to catastrophic and cascading failures. Unless you posit the existence of inter-car communications technology which doesn’t get exist.