Anecdotally: Work in wireless telecom. Tower climbing contractors have shifted to hair tests for drugs because so many applicants try to evade tests, or test positive. They also regularly have issues with people who get their drivers licenses revoked for DUI, to the extent that job postings including "must have current/valid drivers license".
Yes, the people who do the physical installation and maintenance of antennas and lighting on cellular towers, for the most part. Also repair/maintenance for mobile radio systems (public safety), AM/FM radio, etc.
