Futuristic self-driving cars being tested on California roads have needed plenty of old-fashioned human intervention to stay safe.
On Tuesday, California's Department of Motor Vehicles released reports filed by seven companies that received permission to test prototype vehicles starting in September 2014.
The reports show varying levels of progress.
Experts say Google's cars have driven the most distance, and performed relatively well. The company said its cars needed safety-related help 341 times over 424,000 miles. Google said 11 of those instances would have resulted in collisions, and that its cars are not yet ready for the public.
Nissan tested just 1,485 miles in public, but reported 106 cases where the driver had to take control.
A spokeswoman for Nissan did not immediately return a request for comment.
