How safe are self-driving cars?

Following the news that a Tesla driver has tragically died in Florida...

Tesla has confirmed the first fatality involving its autopilot system, as a man in central Florida loses his life in a highway crash.

Joshua Brown died when his Tesla Model S collided with a tractor trailer. He had the autopilot function enabled and was watching a Harry Potter film at the time.

The car manufacturer said:

"What we know is that the vehicle was on a divided highway with autopilot engaged when a tractor trailer drove across the highway perpendicular to the Model S.

"Neither autopilot nor the driver noticed the white side of the tractor trailer against a brightly lit sky, so the brake was not applied

"The high ride height of the trailer combined with its positioning across the road and the extremely rare circumstances of the impact caused the Model S to pass under the trailer, with the bottom of the trailer impacting the windshield of the Model S."


In the wake of the sad news, and with self-driving cars set to become an increasingly common sight on the world's roads, it is understandable that fresh concerns have been raised over the safety of autonomous vehicles.

For its part, Tesla has noted that it is "important" to remember that the system is new technology and still in a public beta phase before it can be enabled.

It must be said that the numbers are still overwhelmingly on Tesla's side.

Elon Musk's company has reported that its autopilot feature has now been used for more than 130 million miles and that, on average, a fatality will occur once every 94 million miles in the US and every 60 million miles worldwide.

In terms of its rivals, Google's autonomous Lexus boasts a quite impressive safety record.

Its first accident report became public in February, when a Lexus hit the side of a bus in California:

"We clearly bear some responsibility, because if our car hadn’t moved there wouldn’t have been a collision. That said, our test driver believed the bus was going to slow or stop to allow us to merge into the traffic, and that there would be sufficient space to do that."

No injuries were reported, however, and the company maintained that its car is still a much, much safer driver than humans.

Until that point, the Google car had driven over two million miles – 1.4 million autonomously – before the first crash that wasn't caused by humans.

Working from a basis that the average driver will be able to sit behind the wheel for 64 years, totalling 862,464 miles over the course of their lifetime, that's a pretty lengthy period without an accident coming to pass.

And yet, getting a comprehensive understanding of the risks – or lack thereof – could be impossible.

According to a report from the RAND research firm in April, self-driving cars can't be tested for enough hours to truly determine their safety.

RAND said that it would need "hundreds of millions of miles and sometimes hundreds of billions of miles" to gain sufficient information to compare the autonomous automobiles with their human-driven counterparts.

This kind of testing would require "tens and sometimes hundreds of years" to carry out.

In a company statement, RAND senior statistician Susan Paddock said:

"The most autonomous miles any developer has logged are about 1.3 million, and that took several years.

"Even if autonomous vehicle fleets are driven 10 million miles, one still would not be able to draw statistical conclusions about safety and reliability."

Looking at the studies that have been done, the University of Michigan Transportation Research Institute found that autonomous cars were almost five times as likely to get into accidents as those driven by humans. The number of injuries were up relatively, but no fatalities were reported.

The October 2015 analysis was based on extensive data from Google and the state of California.

The major takeaway, however, was that the self-driving cars weren't at fault for any of the crashes.

Maybe the safest bet, then, is to eventually get drivers off the wheel altogether...