Special research is being conducted at the University of Southern California under the sponsorship of the National Highway Traffic Safety Administration of the United States Department of Transportation. The research consists of the on-scene, in-depth multidisciplinary investigation of 900 motorcycle accidents to determine cause factors and identify countermeasures. With the acquisition of data from the first 300 accidents, certain critical human elements have been identified as common to a great part of the accidents investigated. The problems of motorcycle conspicuity, rider skill, training and licensing, and protective equipment appear to predominate in accident causation and injury association.