Tri-level study of the causes of traffic accidents: final report. Executive summary.

Abstract

Technical Volume I reports causal factor tabulations from Phases II through V (1972-75). Volume II reports analysis tasks dealing with driver vision, knowledge, psychological make-up, etc. Additional analysis tasks conducted under a contract modification are reported in six separate volumes. Data were collected on three levels. Police reports and other baseline data on the Monroe County, Indiana study area were collected on Level A. On Level B, teams of technicians responded to accidents at the time of their occurrence to conduct on-scene investigations; a total of 2,258 investigations were conducted during Phases II through V. Concurrently, 420 of these accidents were independently examined by a multidisciplinary team on Level C. General population surveys were also conducted. Human factors were cited by the in-depth team as probable causes in 92.6% of accidents investigated in Phases II through V. Environmental factors were cited as probable cause in 33.8% of these accidents, while vehicular factors were identified as probably causes in 12.6%. The major human direct causes were improper lookout, excessive speed, in attention, improper evasive action, and internal distraction. Leading environmental causes were view obstructions and slick roads. The major vehicular causes were brake failure, inadequate tread depth, side-to-side brake imbalance, under-inflation, and vehicle-related vision obstructions. Vision (especially poor dynamic visual acuity) and personality (especially poor personal and social adjustment) were found related to accident-involvement. However, as measured in this study, knowledge of the driving task was not shown to be related.