The report provides extracts from reviews of the scientific literature on drugs and traffic safety, including summaries of what is known about driving impairment from drug use. The review focuses on the similarities and differences in alcohol and other drugs as to effects on driving performance, identification of particular drugs and drug use by body fluid analysis, the involvement of drug use in traffic crashes, and lack of knowledge concerning the extent of drug use (other than alcohol) by drivers and impediments to gaining that knowledge. Information is provided on enforcement, testing, and evidentiary procedures when a violation of chapter 169.121, subd 1 (b) or (c) is alleged (driving while under the influence of a controlled substance or a combination of alcohol and a controlled substance). The report concludes that requiring blood or urine testing in all driving-while-intoxicated (DWI) cases would be counterproductive, because it would divert both police and laboratory resources and reduce the total amount of enforcement of all DWI laws without enhancing drugged driving enforcement. The study recommends that present drug test policies in traffic law enforcement not be changed. Current law provides that drug tests be conducted when there is probable cause to arrest for DWI but alcohol concentration tests show low or no alcohol consumption. 23 references.