The specific letter from NHTSA to Google:<p><a href="http:&#x2F;&#x2F;isearch.nhtsa.gov&#x2F;files&#x2F;Google%20--%20compiled%20response%20to%2012%20Nov%20%2015%20interp%20request%20--%204%20Feb%2016%20final.htm" rel="nofollow">http:&#x2F;&#x2F;isearch.nhtsa.gov&#x2F;files&#x2F;Google%20--%20compiled%20resp...</a><p>... along with an abbreviation I have yet to see previously:<p>&gt;&gt; self-driving vehicles (SDVs)<p>... and their definition of a Level 4 vehicle:<p>&gt;&gt; Google describes its vehicles as having what NHTSA&#x27;s May 2013 Preliminary Statement of Policy Concerning Automated Vehicles calls Level 4 Full Self-Driving Automation.  According to that Statement, a Level 4 vehicle:<p>&gt;&gt; is designed to perform all safety-critical driving functions and monitor roadway conditions for an entire trip. Such a design anticipates that the driver will provide destination or navigation input, but is not expected to be available for control at any time during the trip. This includes both occupied and unoccupied vehicles. By design, safe operation rests solely on the automated vehicle system.