CO HB1146

Creates new criminal offense of "tandem DUI per se" requiring evidence of impaired driving based on observable demeanor and behavior combined with any measurable amount of drug or controlled substance (other than alcohol) in blood or oral fluid within four hours of driving.

Removes the 5 nanogram THC threshold presumption that previously allowed automatic inference of marijuana impairment; now requires behavioral evidence of impairment regardless of drug presence.

Tandem DUI per se is a misdemeanor but becomes a class 4 felony if committed after three or more prior convictions for DUI, DUI per se, tandem DUI per se, or DWAI; includes affirmative defense if defendant consumed drug after stopping driving.

Inactive metabolites of drugs (except benzoylecgonine) do not constitute proof of tandem DUI per se; prosecution must prove drug was consumed before driving stopped.

Makes conforming amendments throughout Colorado Revised Statutes to add tandem DUI per se to licensing sanctions, penalties, prior conviction provisions, and related traffic law provisions; effective September 1, 2019, subject to referendum veto.