Google’s self-driving cars are still some way from becoming roadworthy, according to a new report the company prepared for the California Department of Motor Vehicles.

The report, which looks at all of the test drives said cars undertook from September 24, 2014 to November 30, 2015, reveals that human drivers had to take over control from the autonomous software used to drive the vehicles on 341 separate occasions. Of those, human intervention was needed 272 times due to software or technology failures, while another 69 incidents required people to take control in order to ensure “safe operation of the vehicle”, Google said.

The company added in the report that in two of those incidents, human intervention prevented the car from hitting traffic cones, while in three incidents the problem was caused by other drivers.

As alarming as these incidents sound, Google was quick to play them down in its report, adding that their frequency was declining as its self-driving cars piled up the mileage.

“These events are rare and our engineers carefully study these simulated contacts and refine the software to ensure the self-driving car performs safely,” Google said. “The rate of these simulated contact disengagements is declining even as autonomous miles driven increase. Because the simulated contact events are so few in number, they do not lend themselves well to trend analysis, but, we are generally driving more autonomous miles between these events.”

When we look at the total mileage Google’s self-driving cars have accumulated, the number of incidents does seem rather minimal. Google’s autonomous cars drove more than 1.3 million miles during the period covered by the report, averaging around 30,000 to 40,00 per month. Of those, 424,331 miles were driven on public roads in California, and most of them in a suburban environment around Google’s Mountain View headquarters.

Google said this means its cars are often driving around more complex road systems and intersections than the average human driver would do.

“This differs from the driving undertaken by an average American driver who will spend a larger proportion of their driving miles on less complex roads such as freeways,” Google explained. “Not surprisingly, 89% of our reportable disengagements have occurred in this complex street environment.”

Of course, as much as Google tries to play down the unfortunate incidents involving its autonomous cars, the report doesn’t bode well for promises made by the likes of Elon Musk that self-driving cars will be roadworthy in just two years time.