In both the UK and the US, policy makers are in the process of changing legislation to allow self-driving cars to be used on public roads commercially.

But while the cars are generally regarded as being safe, it has emerged that four autonomous cars have gotten into accidents on Californian roads since September.

Three were cars run by Google, and the fourth was an Audi car.

The leader of Google's self-driving car project wrote in a web post all the accidents have been minor – 'light damage, no injuries' -and happened over 1.7 million miles in which either the car or a person required to be behind the wheel was driving.

'Not once was the self-driving car the cause of the accident,' wrote Google's Chris Urmson.

Almost 50 autonomous cars have been driving around California since September, when the state began issuing permits for companies to test them on public roads.

Two of the four accidents happened while the cars were in control – but from the reports, it appears that the technology was not at fault.

In the other two, the person in the car – who must sit behind the wheel under regulations – was in control, a person familiar with the accident reports told The Associated Press.

Three involved Lexus SUVs that Google outfitted with sensors and computing power in its effort to develop 'autonomous driving,' a goal the tech giant shares with traditional automakers.

The parts supplier Delphi Automotive had the other accident with one of its two test vehicles, which was operated by Audi.

Google and Delphi said their cars were not at fault in any accidents, which the companies said were minor.
Since September, any accident must be reported to the state Department of Motor Vehicles (DMV).

The agency said there have been four, but would not comment about fault or anything else, citing California law that collision reports are confidential.

The person familiar with the accident reports said the cars were in self-driving mode in two of the four accidents, all of which involved speeds of less than 10 mph (16km/h).

The person spoke on condition of anonymity because they were not authorised to discuss the reports publicly.
In the October accident involving Delphi, the front of its 2014 Audi SQ5 was moderately damaged when, as it waited to make a left turn, another car broadsided it, according to an accident report the company shared with AP.

The car was not in self-driving mode, Delphi spokeswoman Kristen Kinley said.

Google, which has 23 Lexus SUVs, would not discuss its three accidents in detail.

Five other companies have testing permits, but all said they had no accidents. In all, 48 cars are licensed to test on public roads.

John Simpson, a privacy project director of the nonprofit Consumer Watchdog, pointed out that Google's ultimate goal is a car without a steering wheel or pedals.

That would mean a person has no power to intervene if a car lost control, making it 'even more important that the details of any accidents be made public – so people know what the heck's going on.'

A major selling point for self-driving cars is safety. Their cameras, radar and laser sensors give them a far more detailed understanding of their surroundings than humans have.

Their reaction times are also faster. Cars could be programmed to adjust if they sense a crash coming – move a few feet, tighten the seat belts, honk the horn or flash the lights in hope of alerting a distracted driver.

A higher priority so far is teaching them to avoid causing a serious accident that could set public and political acceptance of the technology back years, said Raj Rajkumar, a pioneer of the technology with Carnegie Mellon University.

The accidents are not Google's first: In a briefing with reporters a year ago, the leader of Google's self-driving car programme acknowledged three others between when the company first sent cars onto public roads several years ago – without the state's official permission – and May 2014.

In a written statement, Google said that since September, cars driving on streets near its headquarters in Mountain View had 'a handful of minor fender-benders, light damage, no injuries, so far caused by human error and inattention.'

Google said that while safety is paramount, some accidents can be expected given that its cars have gone 'the equivalent of over 15 years of typical human driving,' or approximately 140,000 miles (225,000km).

The national rate for reported 'property-damage-only crashes' is about 0.3 per 100,000 miles (160,000km) driven, according to data from the National Highway Traffic Safety Administration.

In that context, Google's three in about 140,000 miles may seem high. As the company pointed out, however, perhaps five million minor accidents are not reported to authorities each year, so it is hard to gauge how typical Google's experience is.

Three other states have passed laws welcoming self-driving cars onto their roads. Regulators in Nevada, Michigan and Florida said they were not aware of any accidents.