The statistics gathered by the National Police Administration of the Ministry of the Interior indicates that in the year of 1999, totally 2,487 of the traffic accidents reported in Taíwan fall into the A1 category (death and serious injury), with 2,393 persons killed and 1,636 seriously injured. After a traffic accident, the parties concerned will often ask an expert investigation to be conducted to clearly define which party to be held responsible for the accident. Right now in Taiwan, when analyzing causes of a traffic accident, the traffic accident investigation committee will make judgement mainly according to the right of way and the rules and regulations related to driving behavior, such as Regulations Regarding Road Traffic Control and Penalty for Violation, Road Traffic Safety Regulations, and Rules for Road Signs and Signals. In this research, we studied literature and collected information through questionnaires. The purpose of this research is to find out the thinking procedures of the traffic accident investigation committee when they analyze accident causes. We tried to categorize traffic accidents according to types of accident and types of collision, and we also combined the right of driving behavior, the right of way, and the rules and regulations regarding infringement of rights and other violation behaviors. By means of the decision analysis procedures, we aim to construct a decision support system for analyzing accident causes, so that persons in charge of handling accidents, members of the investigation committee and parties concerned may have something objective to refer to when analyzing accident causes and trying to find applicable traffic rules and regulations.