"Few employers have used impairment testing, and information concerning that experience is very limited and extremely difficult to obtain. The available information, however, indicates that impairment testing is not just a better answer on paper, but in practice as well. Employers who have used impairment testing consistently found that it reduced accidents and was accepted by employees. Moreover, these employers consistently found that it was superior to urine testing in achieving both of these objectives."
National Workrights Institute, "Impairment Testing: Does It Work?" (Princeton, NJ: NWI, undated).