In Multidisciplinary Accident Investigations, each of the elements of the transportation system is studied in depth. This paper identifies the methodology developed by the Southwest Research Institute Multidisciplinary Accident Investigation team for analyzing contributory elements of the human component in a highway collision. To accomplish accurate analysis, detailed and factual demographic, medical and psychological information is obtained through interviews with the accident participants, and/or their families, friends, neighbors and employers;​ assessment of driving, credit, school, and other records;​ and consultation with appropriate specialists. Useful forms have been developed for reporting such psychological and injury data. The findings for eighty-two Southwest Research Institute case studies have been summarized with special emphasis given to the role of the human/psychological factors. Brief case histories are used to illustrate salient points.