tldr; Impairment detection methods are currently too inaccurate to use (both false positive and false negative).

And then if anything is ever accurate enough they'll have to create testable standards that car manufacturers can easily implement.

And NHTSA is concerned with security and privacy issues as well. They'll keep updating congress on progress once a year.

My take is it's very possible the rule may never get made.

[1] https://www.nhtsa.gov/sites/nhtsa.gov/files/2026-03/Report-t...