Google revealed on Monday that 11 of its self-driving cars have been involved in minor traffic accidents since it began trialling the technology six years ago.
Four of the 48 self-driving cars on the roads of California, operating under licences issued since September 2014, were involved in collisions in the last eight months, as shown by figures from the state's Department of Motor Vehicles.
Of those cars, three belonged to Google while the fourth was operated by Delphi. According to both companies their vehicles were not at fault. Under Californian law such details remain confidential.
Google said its driverless cars had never been the cause of an accident and that it has avoided many major accidents over 1.7 million miles (2.8 million km) travelled, including nearly one million in self-driving mode.
The company revealed the number after Associated Press initially reported the figures. Google’s director of self-driving cars Chris Urmson wrote in a blog post that all 11 accidents were minor, with “light damage, no injuries”.
“Not once was the self-driving car the cause of the accident,” Urmson wrote.
However, critics warned that transparency is needed to assure the public that the nascent fleets of self-driving cars are safe.
The national rate for reported “property damage-only crashes” is about 0.3 for every 100,000 miles (160,000km) driven, according to the National Highway Traffic Survey.
Apparently Google’s numbers would fall under that benchmark – even though 11 accidents over 1.7 million miles would be 0.6 for each 100,000 miles – because as many as five million accidents go unreported each year, the company said.
“Even when our software and sensors can detect a sticky situation and take action earlier and faster than an alert human driver,” Urmson wrote, "sometimes we won’t be able to overcome the realities of speed and distance. Sometimes we’ll get hit just waiting for a light to change.”