California started allowing self-driving cars to hit public roads for testing in September. Already, there have been four accidents involving these cars, the Chicago Tribune reports.

Two of the accidents occurred when the cars were operating under their own control and the other two occurred when a person was behind the wheel driving the cars, a person familiar with the accident reports told The Associated Press.

Out of the four accidents, three involved Lexus SUVs that Google outfitted with sensors and computers in an attempt to develop a self-driving car. Parts maker Delphi Automotive had the other accident with one of its two test vehicles.

Both Google and Delphi said their cars were not at fault in the minor accidents.

All accidents that occur must be reported to the state's Department of Motor Vehicles. The DMV says that there have been four of these accidents but would not release any more details because California law says that collision reports are confidential.

Two of the four accidents occurred when the cars were in self-driving mode, the person familiar with the accident reports said. These two accidents occurred when the cars were traveling less than 10 mph.

Besides Google and Delphi, five other companies have been testing out self-driving cars. These companies have all told the AP that they have not had any accidents yet. In total, there are 48 cars that are licensed to be tested on public roads.

The public is worried that these accidents have been kept from them. They say that people should be able to see these reports.

John Simpson, privacy project director for nonprofit Consumer Watchdog, said Google wants to create a self-driving car with no steering wheel or pedals. This means that if the car loses control, a person would have no way to take over the controls to prevent a crash.

Samspon says that any accidents that have occurred with these cars should be released to the public so that they know what is going on with them.

The main focus of self-driving cars is supposed to be safety. The cameras and sensors are designed to give them better information on the roads and to react faster than a human can. The cars can be programmed to move over to avoid crashes, tighten seat belts, honk the horn or other crash-preventing activities.

Google acknowledged that some accidents could happen since their cars have been tested for about "15 years of typical human driving" (about 140,000 miles).

The accidents have all been very minor with just property damage resulting, The Verge reports.