The NHTSA found that Tesla cars with Autopilot activated have 40% fewer accidents.
http://www.businessinsider.com/tesla-autopilot-cuts-crash-rates-by-40-government-finds-2017-1
Here is some further discussion about the 40% claim.
https://www.autoblog.com/2018/05/03/nhtsa-disputes-tesla-safety-claim-autopilot/
https://arstechnica.com/cars/2018/05/sorry-elon-musk-theres-no-clear-evidence-autopilot-saves-lives/