New data has shown that self-driving car prototypes do not require as much human help as previously thought as they are getting better at navigating California streets and highways without a human backup driver intervening.

The data by California transportation regulators that was made public earlier this week reveal safety-related incidents reported by 11 companies that have been testing more than 100 vehicles on public roads, primarily in the Silicon Valley neighborhoods where the technology has grown up. The documents catalog the number of times from December 2015 through the end of November that humans took over control from a car’s software for safety reasons.

Waymo, which is Google’s self-driving car project rebranded, was the front runner as far as testing of driverless cars go and reports indicate they had much greater success than any other companies. Its fleet drove itself more than 635,000 miles with 124 safety-related “disengagements,” which must be reported when the technology fails or the backup driver takes control out of concern the car is malfunctioning. The Google project’s disengagement rate was the equivalent of two incidents every 10,000 miles, a notable decrease over the prior year, when there were eight disengagements per 10,000 miles.

Nissan on the other hand reported 28 disengagements over 4,099 miles, or 68 incidents per 10,000 miles – far better than the 106 in 1,485 miles (713 per 10,000 miles) it reported last year.

Cruise Automation, a startup acquired last year by General Motors, reported driving the second most test miles this year. Cruise said its prototypes had 181 disengagements over 9,776 miles (185 per 10,000 miles) and that it was “pleased with our progress” during testing on the complex streets of San Francisco. The company did not file numbers for 2015 because it did not have a testing permit that year. Though imperfect, the data represent the best peek the public gets into the secretive and fiercely competitive world of self-driving cars and how the prototypes are performing.

California required the disengagement reports as part of regulations governing testing on public roads. Separately, the state also requires companies to report any collisions involving its cars. When the technology will be ready for the public depends on several factors, including regulators’ readiness and company confidence the vehicles are safe. While Tesla’s Elon Musk has been bullish, talking about months rather than years, companies such as Waymo have suggested 2017 or 2018 is more realistic.

Tesla’s disengagement report said four prototypes drove a total of 550 miles last fall, experiencing 182 disengagements – the equivalent of 3,309 disengagements every 10,000 miles. Tesla logged the miles primarily to develop a publicly posted video, set to the Rolling Stones song “Paint It Black,” of the driver’s seat perspective in a car where a person does not have to put their hands on the wheel or feet on the pedals. The video promoted how Tesla was shipping cars with advanced sensors that will be activated in the future. Generally, Tesla tests on private land, not public roads. Those disengagements are not reported to the state.

Meanwhile, Tesla is gathering tens of millions of miles of real-world data when owners engage the current Autopilot feature, which can control steering and speed but is not sophisticated enough to make the cars self-driving from the regulatory perspective.

California’s Department of Motor Vehicles has been working for several years on regulations that will govern how the technology can be rolled out to the public when companies believe testing shows it is ready.

The state expects to release final “public operation” regulations within six weeks, according to Melissa Figueroa, a spokeswoman for California’s State Transportation Agency.