Even though the technology behind autonomous vehicles has progressed hugely in recent years, it's still by no means perfect. A long list of companies are still testing their electric vehicles in California to improve software capabilities and safety. Disengagements are a key part of the testing process and they occur when a car's software detects a failure or a driver perceives a failure, resulting in control being seized.According to data from the California DMB published by website The Last License Holder , 28 companies reported that they were actively testing cars on public roads in the state. In total, they operated 467 vehicles and covered just over 2 million miles in automomous mode with 143,720 disengagements occurring. When it comes to flawless autonomy, Google's Waymo is way ahead of the pack with its fleet covering 1.27 million miles last year with 11,154 miles per disengagement.That's better than many companies attempting to perfect the technology, especially heavyweight competitors like Uber and Apple . Last year, Ubers cars drove nearly 27,000 miles and only managed 0.4 miles per disengagement. Apple has a similar performance with 1.1 miles per disengagement out of 80,000 miles recorded in total.