This paper provides final results of an accident investigation project conducted by the Indiana University Institute for Research in Public Safety (IRPS), for the National Highway Traffic Safety Administration, emphasizing particularly the role of vehicular factors in causing accidents. In addition, these results are put in context with other recent studies which have provided information on the same topic.Data collection for the Indiana University accident causation study was confined to Monroe County, Indiana, where between 1970 and 1975, 2,258 accidents were investigated by teams of technicians using a consistent set of procedures and terminology. Concurrently, 420 in-depth investigations were conducted by a multidisciplinary team.Vehicular degradations, malajustments, and failures were identified as definite causes in 4.5% of these accidents by the multidisciplinary team, and in 4.1% by the technicians. Vehicular problems were considered either definite or probable causes in 12.6% of these accidents by the in-depth team, and in 9.1% by the technicians. Problems with brakes and tires predominated as vehicular causes, with gross brake system failure and inadequate tread depth being two of the leading problems identified.The other studies referenced, while varying somewhat in the proportion of accidents in which vehicular factors were implicated, also reflect brakes and tires as predominant problem areas.