Google is promising to give monthly updates about accidents involving its driverless cars.
Its report for May detailed that Google cars have been involved in 12 crashes since it first began testing in 2009, mostly when they were hit from behind.
Reuters reports that a further crash this month takes the total to 13 accidents but that Google insists none was caused by a fault with its cars.
American organisation Consumer Watchdog called for more details on the accidents, including statements from witnesses and other drivers. It suggested that the rear-ending could be because vehicles stop quicker than human drivers expect, although Google disputes that saying most occurred when the vehicle was stopped.
Reuters further reports that Google is about to take its pod-like prototype vehicles off the test track and on to the roads of Mountain View, California, this summer. The company described the two-seater car as “the world’s first fully self-driving vehicle.”
Last week at the ITS America annual meeting in Pittsburgh, the head of the project Dr Chris Urmson repeated his intention to have the cars commercially-available within five years.