In November 2008 and again in March 2009, an expert panel was convened by the National Highway Traffic Safety Administration with the goal of determining whether a list could be developed to indicate which medications or classes of medications may pose a hazard to driving. There was particular interest in having the panel develop a list of "safe" medications that do not impair driving. The value of the list would be to better inform patients and physicians regarding the likely effects of a drug on driving. This information could lead to better-informed prescribing practices and to more rational selection of medications by patients. The panel was composed of an international group of behavioral scientists, epidemiologists, pharmacologists, toxicologists, and traffic safety professionals to provide a broad-based perspective on the issue. Discussions included prescription (Rx) medications as well as over-the-counter (OTC) medications and illicit drugs. Although illicit drugs are best known for their impairing effects, Rx and OTC medications are also known to be capable of producing impairment and many are frequently encountered in impaired driver populations. The panel agreed that one of the barriers to categorizing drugs with respect to driving impairment risk is the lack of a common, standardized protocol for assessing the impairing potential of drugs. The panel recognized the need for a structured, standardized protocol for assessing the driving impairment risk of drugs that would lead to better classification of drugs in terms of driving impairment risk. The approach could be useful in providing more meaningful precautions for users and prescribers regarding the impact of drugs on driving. This report provides the background for the project and assembly of the expert panel, a description of the proposed protocol, and offers examples of how the protocol could be useful in evaluating a drug.