I think when you say they "fail", I think you are referring to the disengagements, right? The report you link to there says:
“Immediate manual control” disengage thresholds are set conservatively. Our objective is not
to minimize disengages; rather, it is to gather as much data as possible to enable us to improve our
self-driving system.
Also, table 4 reports the number of disengagements (for any reason) each month, as well as the miles driven each month. In the most recent month in that table, it's actually 16 disengagements over 43275.9 miles. That's approximately one disengagement every 2705 miles; about the distance from Sacramento, CA to Washington, DC. At the start of 2015 it was only 343 miles per disengagement; 53 disengagements over 18192.1 miles. The pace of improvement is incredible, especially considering disengagements are set conservatively.
Can a human drive from Sacramento CA to Washington DC without a single close call or mistake along the way? I really doubt it. This technology will be saving lives soon.
