The Studies address issues raised in Section 2013 of the Safe, Accountable, Flexible, Efficient Transportation Equity Act: A Legacy for Users (SAFETEA-LU), which was enacted in 2005. It directs the Secretary of Transportation to advise and coordinate with other Federal agencies on how to address the problem of driving under the influence of an illegal drug; to conduct research on the prevention, detection, and prosecution of driving under the influence of an illegal drug; and to submit to Congress a report on the problem of drug-impaired driving. In addition to addressing impaired driving under the influence of illegal drugs, studies also include impaired driving under the influence of prescription and over-the-counter legal drugs. Issues addressed by the studies include the determination of which drugs impair driving; the difficulties in relating blood levels of drugs to degree of impairment; the lack of information on which drugs are frequently used by drivers and which drugs elevate crash risk; and problems in obtaining representative data about current enforcement, prosecution, and adjudication of DUID. This report also describes three levels of training for law enforcement officers that address signs that a driver is drug-impaired, reviews DUID laws, and discusses what is known about the role of drugs as causal factors in traffic crashes. The report cites the need for additional research, particularly regarding the need for better data and information systems that allow continued progress in understanding and addressing the DUID problems. There is a need to have statewide arrest or disposition data that distinguish drug-impaired driving cases from alcohol-impaired driving. Recommendations are offered for developing a model statute on DUID. 36 references