A better way of keeping impaired drivers off the road, or out of a safety-sensitive workplace, is to use performance testing.
A performance test doesn't measure what is in your bloodstream, it measures your hand-eye coordination, reaction time, and other indicators of your current driving ability.

Drug tests can only pick up substances they test for, so someone impaired on an unusual drug, or a prescription, will typically escape detection. Also, a performance test will detect any kind of impairment, including that which that doesn't relate to substance use, such as fatigue, hangover or emotional upset.

Roadside performance testing is already common. When a police officer asks a driver to walk a straight line, touch his nose or count backwards, the driver is being tested for his ability to perform, regardless of what may be in his bloodstream. However, this kind of testing is subjective and not standardized.

One standardized performance test gaining popularity in the workplace is a computer-based "critical tracking test." This test has the user use a knob to try to keep a randomly veering cursor centered on a video screen. This kind of testing is cheaper, faster and more accurate than urine testing for determining current impairment. This kind of simple test could easily be adapted for roadside use, and given by police to drivers suspected of any sort of impairment.

Links:

* Alternatives to Drug Testing. Non-testers List.
www.nontesterslist.com/nontesters/ptest.html

* Performance testing can add an extra measure of safety. HR Magazine, February 1996
www.findarticles.com/p/articles/mi_m3495/is_n2_v41/ai_18159115

* Daily Skill Test System checks hand-eye coordination. NORML PotPourri, February 1995
www.pdxnorml.org/performa.html

* An Alternative to Drug Testing. Inc Magazine, April 1995
www.inc.com/magazine/19950401/2235.html