No, you don't need to drive a billion miles to test a robocar
Submitted by brad on Thu, 2017-07-20 13:47Earlier I noted that Nidi Kalra of Rand spoke at the AVS about Rand's research suggesting that purely road testing robocars is an almost impossible task, because it would take hundreds of millions to a billion miles of driving to prove that a robocar is 10% better than human drivers.
(If the car is 10x better than humans, it doesn't take that long, but that's not where the first cars will be.)
This study has often been cited as saying that it's next to impossible to test robocars. The authors don't say that -- their claim is that road testing will not be enough, and will take too long to really work -- but commenters and press have taken it further to the belief that we'll never be able to test.
The mistake is that while it could take a billion miles to prove a vehicle is 10% safer than human drivers, that is not the goal. Rather, the goal is to decide that it's unlikely it is much worse than that number. It may seem like "better than X" and "not worse than X" are the same thing, but they are not. The difference is where you give the benefit of the doubt.
Consider how we deal with new drivers. We give them a very basic test and hand them a licence. We presume, because they are human teens, that they will have a safety record similar to other human teens. Such a record is worse than the level for experienced drivers, and in fact one could argue it's not at all safe enough, but we know of no way to turn people into experienced drivers without going through the risky phase.
If a human driver starts showing evidence of poor skills or judgments -- lots of tickets, and in particular multiple accidents, we pull their licence. It actually takes a really bad record for that to happen. By my calculations the average human takes around 20 years to have an accident that gets reported to insurance, and 40-50 years to have one that gets reported to police. (Most people never have an injury accident, and a large fraction never have any reported or claimed accident.)