Based on the data in the documents, the drivers had to take over from the self-driving system every mile for one reason or another. They include navigation issues related to unclear lane markings, the system missing a turn or bad weather preventing it from working properly. Drivers also had to take over due to auto-detected hard decelerations or abrupt car jerks more frequently last week than in January.

Uber didn't count events that might have led to serious accidents, such as those that would have damaged property or hit a person -- those were counted as "critical interventions." Thankfully, the vehicles drove an average of 200 miles between these critical interventions last week. The average used to be 114 miles between each one, so there's definitely some improvement. But Uber testers didn't see a steady rate of progress either, since the average seems to dip and rise back up.

The ride-hailing firm is currently testing its autonomous vehicles in Pennsylvania, Arizona and California, though a lawsuit filed by Google could put a stop to the trials. Google is accusing Otto, an autonomous trucking company Uber acquired last year, of using materials stolen from Mountain View's self-driving car division Waymo. It's now asking the court to block the firm's autonomous car operations.