I've written about this before, way back in some now gone version of Butch's TreeHouse. As a USFS employee, carrying certification to use a firearm on duty, I was subject to random drug tests.
The rules said, I had to report to the contract lab within 2 hours of notification, or was considered non-responsive and thus guilty by default.
The lab was on the west side of Portland, well over an hour from my official duty station...and my normal work took me from 45 minutes to 120 minutes farther out in the field beyond that.
I got the call twice, relayed over the USFS radio net. I did head in, but I never made it on time...in fact, I never made it to the lab at all. Both times, my supervisor intervened and said I was not in a location to be able to meet the legal demands.
Pretty dumb setup, and all focused on peeps that work in town. Policy makers live in the urban environment, with full time cell service. Not so much, for most of us on the ground grunts.
I am sure I was far from the only Forest Service employee that found themselves in a similar situation.