Accident rates are twice as high for driverless cars as for regular cars, according to a study by the University of Michigan’s Transportation Research Institute in Ann Arbor, Michigan. However, self-driving vehicles were not at fault in any of the incidents looked at. Typically, they were hit from behind in slow-speed crashes by human drivers who were unaccustomed to other road users moving with such caution.
“They’re a little bit like a cautious student driver or a grandma,” said Dmitri Dolgov, principal engineer of Google’s driverless cars project, speaking to Bloomberg.
In November, one of Google's cars was pulled over for driving too slowly in Mountain View, California. Moving at 24mph in a busy 35mph zone, traffic was backing up behind.
“The right thing would have been for this car to pull over, let the traffic go and then pull back on the roadway,” said Sergeant Saul Jaeger, head of the police department’s traffic-enforcement unit. “I like it when people err on the side of caution. But can something be too cautious? Yeah.”
More recently, also in Mountain View, a self-driving Google car attempted to turn right on a red light – a legal manoeuvre, but a complex one necessitating that it assess the movement of traffic from multiple directions. The car came to a stop, switched on its indicator and began creeping slowly into the junction to get a better look. Another car stopped behind it and also began rolling forward, but rear-ended the Google car at 4mph.
Brandon Schoettle, co-author of the Michigan study, said that other incidents have been caused by sudden, unexpected braking. “These vehicles are either stopping in a situation or slowing down when a human driver might not,” he said. “They’re a little faster to react, taking drivers behind them off guard.”
Dolgov says Google are now looking to make their driverless cars more ‘aggressive’ while still operating according to traffic laws. He believes this is necessary so that they can fit into traffic more naturally, meaning that human drivers will be better able to predict their behaviour. “Driving is a social game,” he said.
Earlier this year, the Commons transport committee said that the Department for Transport (DfT) needed to prepare for a transition period when autonomous vehicles first come into use. It pointed out that the full benefits of driverless technology cannot be realised until there is wide uptake. AA president Edmund King described that period as being ‘a potential nightmare.’