A preliminary study from the University of Michigan Transportation Institute took a look at autonomous vehicle crashes reported by Google, Delphi, and Audi, all of which have licenses to operate self-driving vehicles in a number of states. The researchers, Brandon Schoettle and Michael Sivak, compared that data to adjusted statistics pertaining to conventional vehicles. The study showed that self-driving vehicles were actually involved in more accidents on average, per million miles traveled, than their conventional forebears.

However, the researchers cautioned that those numbers may not tell the whole story. The data was pulled from 11 crashes among three makers of self-driving cars whose fleets only cumulatively drove 1.2 million miles on public roads. The data for conventional cars, however, was derived from a sample of the reported crashes that occurred over 3 trillion miles of annual driving. (The researchers did, however, adjust the data to account for unreported crashes.)

Because of the statistical uncertainty that comes with comparing a census of autonomous vehicle crashes with a sample of conventional vehicle crashes, the researchers couldn’t say for sure that self driving vehicles are more likely to be involved in crashes than conventional cars.

What the analysis did find, however, was that every crash an autonomous vehicle was in was caused by a driver of a conventional car. In addition, 73 percent of the crashes involving an autonomous vehicle happened when the car was going 5 mph or less, or while the car was stopped.

While 15.8 percent of crashes involving conventional cars involved a fixed object and 14 percent of crashes involving conventional cars involved a non-fixed object (like a pedestrian jay-walking), autonomous cars only ever collided with another vehicle. In addition, 3.6 percent of conventional vehicle collisions were head-on crashes, but autonomous vehicles have only thus far suffered a rear-end collision, a side-swipe, or an angled collision.

Less than 1 percent of conventional vehicle crashes involved a fatal injury, but no autonomous vehicles have recorded a fatal injury. 28 percent of conventional vehicle crashes resulted in a non-fatal injury; only 18.2 percent of autonomous vehicle crashes resulted in the same kind of injury. By far, the largest result of autonomous vehicle crashes was property damage, at 81.8 percent.

Overall, the preliminary data showed that self-driving vehicles resulted in fewer injuries per crash than conventional vehicles, but only when the data was adjusted for unreported crashes in conventional vehicles.

Still, the preliminary study shows that self-driving cars are not a panacea for vehicle collisions, at least while traffic on the roads is mixed between autonomous and self-driving cars.