Is Waymo really years ahead of Cruise? Given the different environments they're testing in, I'm not sure it's clearcut to compare how well the two are doing relatively.
It is hard to say how similar different companies are when deciding what counts as a disengagement that needs reporting, but if the headline numbers are accurate, having twice as many disengagements per mile is extremely impressive; the SF environment is far more than twice as hard to drive in as suburban / highway environments.
