[ARCHIVE ANSWER]

If you refuse the swab, it is treated as an automatic admission of guilt, and you get the
maximum penalty. For first timers, it is a one-year loss of license and a $1,500 fine. Not
every car has them yet, but they will soon. Currently, they have a special van at
roadblocks, placed where you can’t see them until it’s too late. They are in use in select
areas and contexts, such as parolees and probationers.
In Phoenix, Arizona, they can take your blood and have a mobile unit just for that. If you
refuse, you lose your license. You consent to this by application for said licenses. I don't
see why a swab won't be implemented similarly since behavior profiling will likely be
fine tuned by law enforcement to differentiate potential drug users to swab up.