Los Angeles - Four of the nearly 50 self-driving cars now rolling around the state of California have gotten into accidents since September, when the state began issuing permits for companies to test them on public roads.Two accidents happened while the cars were in control; in the other two, the person who still must be behind the wheel was driving, 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 aggressive 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.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. 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 16km/h. The person spoke on condition of anonymity because they were not authorised to discuss the reports publicly.Five other companies have testing permits. In response to questions from the AP, all said they had no accidents. In all, 48 cars are licensed to test on public roads.The fact that neither the companies nor the state have revealed the accidents troubles some who say the public should have information to monitor the rollout of technology that its own developers acknowledge is imperfect.John Simpson, a longtime critic of Google as privacy project director of the nonprofit Consumer Watchdog, pointed out that the company'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 chief 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 also should be faster. Cars could be programmed to adjust if they sense a crash coming - move a few metres, 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.