Four self-driving cars out of about 50, now moving around California, have met with accidents since September. The state started issuing permits for companies in September so as to test them on public roads.

Three cars included Lexus SUVs; Google outfitted them with sensors and computing power in its attempt to develop 'autonomous driving', a combined goal of the company and traditional automakers. Delphi Automotive also reported an accident in which one of its two vehicles was involved.

Bryant Walker Smith, a law professor at the University of South Carolina, who has expressed his views extensively on the technology, said that these cases will occur if there is some sort of fault in self-driving cars.

According to Smith, "For a lot of reasons more might be expected of these test vehicles and of the companies that are deploying them and the drivers that are supervising them than we might expect of a 17-year-old driver in a 10- year-old car".

According to Google and Delphi, there were no faults in their cars in any accidents. Any accident since September is needed to be reported to the state Department of Motor Vehicles. According to the agency, there have been four accidents, but they would not mention regarding fault or anything else, referring to California law, according to which, accident reports could not be revealed.

According to data from the National Highway Traffic Safety Administration, the national rate for reported 'property-damage-only crashes' is approximately 0.3 per 100,000 miles driven. Google said that safety is their priority, but still some accidents could take place.