Eleven driverless vehicles have been involved in minor accidents on California roads over the past six years during testing, Google said Monday, stressing that none of its cars were at fault in any of the incidents.

The company made the admission after a reported from the Associated Press said two Google driverless cars, while controlled by computers, were involved in accidents since last fall when the state gave the company official permission to start testing the technology on public roads. Nobody was hurt in any of the crashes, Google said.

But in the wake of the accidents, the police reports were not made public in accordance with California law. Google did not release the reports either — a practice could hurt the very future of driverless cars that several technology companies are trying to build.

Proponents of self-driving cars argue that computer-driven vehicles can help improve automotive safety by reacting more quickly to oncoming dangers and keeping a better eye on the environment, reducing the risk of driver error. But the public lacks objective data about whether that’s true in practice or even potentially true.

Earning drivers’ trust is going to be one of the biggest challenges for driverless car manufacturers. Giving up the steering wheel to a computer just won’t come naturally to many people. Nor will the prospect of having to share the road with machines that can make their own decisions.

”Safety is our highest priority,” said Google in a statement. “Since the start of our program six years ago, we’ve driven nearly a million miles autonomously, on both freeways and city streets, and the self-driving car hasn’t caused a single accident.”

Add it all up and the message seems pretty clear: The autopilot was not the problem.

But what would really bolster people’s confidence is if the companies could prove that the autopilot performed well at preventing or avoiding a crash — not merely that it wasn’t the cause of a crash.

In two of the crashes, according to the AP, the driverless car features were engaged and no human was behind the wheel. Understanding exactly how the self-driving cars behaved under these conditions — and in similar situations to come — will be the key to showing whether driverless cars really are better or safer than humans behind the wheel.

Imagine a world in which driverless cars are the only types of car on the road. In this hypothetical universe, driverless cars are completely safe. Each vehicle behaves predictably according to its programming, so the interactions between those cars become predictable events as well. In this universe, the inattentiveness, speeding, road rage and the half-dozen other reasons accidents happen today would have been eradicated.

The world we inhabit today is far messier. For the foreseeable future, self-driving cars will have to respond to all the crazy things human drivers do, such as cutting other people off, texting behind the wheel, or driving drunk.

If the police reports show there was nothing the autopilot could have done to prevent a crash, that’s a clear point in favor of driverless car manufacturers — especially if the reports also suggest that a human driver would have fared no better.

But suppose the crashes involved a head-on collision with an 18-wheeler whose lights were flashing and horn was blasting, and the driverless car missed all the signs. That would be a big problem.

The fact that we don’t really know, and that the state of California won’t release the reports, could become a setback for the adoption of driverless cars. We are left with voluntary disclosures by individual manufacturers to fill the gap. On Monday, Google published a post explaining that its cars have been in 11 “minor” accidents, 7 of which occurred when another driver rear-ended them. The blog post also highlights cases where the autopilot successfully avoided crash risks even as other drivers were behaving dangerously in the situation. But the full police reports were not released.

This type of crash and near-crash information, particularly on a large scale, could help consumers make informed decisions about whether to get a self-driving car if and when they finally make it to market.