  Between June 2018 and December 2022, Tesla released quarterly safety reports
citing average miles between crashes for Tesla vehicles. Prior to March 2021,
crash rates were categorized as 1) with their SAE Level 2 automated driving
system Autopilot engaged, 2) without Autopilot but with active safety features
such as automatic emergency braking, and 3) without Autopilot and without
active safety features. In January 2022, Tesla revised past reports to reflect
their new categories of with and without Autopilot engaged, in addition to
making small adjustments based on recently discovered double counting of
reports and excluding previously recorded crashes that did not meet their
thresholds of airbag or active safety restraint activation. The revisions are
heavily biased towards no-active-safety-features$\unicode{x2014}$a surprising
result given prior research showing that drivers predominantly keep most active
safety features enabled. As Tesla's safety reports represent the only national
source of Level 2 advanced driver assistance system crash rates, clarification
of their methods is essential for researchers and regulators. This note
describes the changes and considers possible explanations for the
discrepancies.
