Accident Causation Factor Analysis of Traffic Accidents on the Example of Elderly Car Drivers Using the Causation Analysis Tool ACAS

The need of in-depth accident causation data in accident research is becoming more and more important. The German In-Depth Accident Study (GIDAS) is well qualified to deliver adequate data to conduct an investigation on this field, based also on identifying the causes of accidents. This led to the development and implementation of a special tool called ACAS (Accident Causation Analysis System) for the collection of such causation data adopting the GIDAS methodology. Using this system, for each accident participant one or more of five hypotheses of human cause factors are formed along the basic human functions active when managing a situation in traffic. These hypotheses are subsequently specified by appropriate verification criteria. To facilitate the analysis of accident causes, the information collected with ACAS is recorded in a structured code of digits. With the help of structured questionnaires for on-scene investigation used for interviews of accident participants, it is possible to easily identify human failures and categorize these in the ACAS structure. Internal analysis of the herewith coded accident causation information has proven that with this system it is possible to find causes of traffic accidents with enough details to identify differences of psychological performances categorized by the basic human functions in the situation or the emergence of the accident. Past studies on identifying typical accident scenarios of elderly traffic participants have shown that it is difficult to find typical circumstances and features of accidents caused by the elderly, based on classic accident research data. With the present study a first step in this direction is done by analyzing the causation coding of accidents with personal damages of n=817 non-elderly car drivers (aged 25-64) with failures of one of the five human causation categories and to n=169 elderly car drivers aged 65 and over (total of 986 for both age groups). The focus of this study lies on identifying the special causes of elderly traffic participants and analyzing the psychological effects which lead to failures in the situation of the accident event. The results of the causation analysis display that with elderly traffic participants the human failures are mostly about perception problems and difficulties with the execution of a desired action. The study also revealed that the causation category of an accident has an influence on the accident severity (injury outcome). This is an important factor which has to be kept in mind when looking for countermeasures to decrease severe injuries or fatalities. The knowledge about the human failures is an essential part e.g. for the development of driver assistance systems.