Bad news for companies that include Alphabet Inc. (NASDAQ: GOOGL), Ford Motor Co. (NYSE: F) and Tesla Motors Inc. (NASDAQ: TSLA). According to a new paper, “How Many Miles of Driving Would It Take to Demonstrate Autonomous Vehicle Reliability?” issued by the research company RAND Corporation, self-driving cars have been insufficiently tested to tell whether they are safe.

The research is a blow to the self-driving car industry, which has claimed that cars driven by humans are more dangerous than those driven by machines. These companies likely have spent hundreds of millions of dollars producing these cars as the future of auto transportation.

According to the paper:

Given that current traffic fatalities and injuries are rare events compared with vehicle miles traveled, we show that fully autonomous vehicles would have to be driven hundreds of millions of miles and sometimes hundreds of billions of miles to demonstrate their safety in terms of fatalities and injuries. Under even aggressive testing assumptions, existing fleets would take tens and sometimes hundreds of years to drive these miles — an impossible proposition if the aim is to demonstrate performance prior to releasing them for consumer use. Our findings demonstrate that developers of this technology and third-party testers cannot simply drive their way to safety.

Also:

Developers of this technology and third-party testers will need to develop innovative methods of demonstrating safety and reliability.

Even with these methods, it may not be possible to establish with certainty the safety of autonomous vehicles. Uncertainty will remain.

Anecdotally, self-driving cars have been in a few well-publicized accidents, which have led to concerns about their safety. Among these was an accident in February between a Google self-driving Lexus sport utility vehicle and a bus. The accident was minor, but it still set off alarm bells about the potential need for human drivers.

So it seems that, as the self-driving car industry grows, it cannot say for certain whether these new autos are safe.

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