Driverless cars are racking up more than double the number of accidents as conventional cars with a human behind the wheel.
But "it's a complicated message," says Brandon Schoettle of the University of Michigan Transportation Research Institute.
His study shows that driverless cars get in 9.1 crashes per million miles driven.
But here's the really interesting part. The accidents have all been minor - the worst injury was whiplash - and the crashes were all caused by human drivers plowing into the back of the driverless cars.
Apparently human drivers are not very good at interacting with cars that always obey the law.
Conventional cars with a driver behind the wheel get in only 4.1 accidents per million miles driven - but some of those accidents are fatal.
So the research actually supports the hypothesis that driverless cars are safer overall, because they always drive cautiously, don't get distracted, and obey speed limits.
Most of the data involves Google's fleet of driverless cars, which are being tested on public roads.
Google issued this statement in response to the study:
In more than 1.3 million miles of autonomous driving since the start of our project in 2009, not once has our self-driving car been the cause of a collision. We publish the details of all crashes we’ve been involved in on our website each month, and there’s a clear theme of human error and inattention. The researchers themselves concede in their report that the actual crash rates of for self-driving vehicles could be lower than for conventional vehicles.”
