If involved in crashes, they are not chemically tested for drugs other than alcohol. Conservative estimates suggest that thousands die and tens of thousands are injured annually as a result of drug-impaired driving. In a 1988 study by the University of Tennessee Medical Center that analyzed urine samples of crash-injured drivers, drugs other than alcohol were detected in 40 percent of the samples. Many drug users routinely abuse more than one drug simultaneously. This practice, known as poly-drug use may be more common than single drug use in certain settings.
Many drug abusers drink alcohol to disguise their use of drugs.
Poly-drug use can produce a synergistic impairment of the user's ability to drive. This condition is particularly deadly and is prevalent among younger drivers. More than half had consumed a drug or drugs other than alcohol. To reduce the highway mortality rate from alcohol and drug impairment requires altering culturally rooted behaviors. Behavior-al change may best be accomplished through ongoing programs of vigorous enforcement, coupled with ambitious education and information activities.