An Event Tree Screening Approach for Transportation Risk Analysis

Event trees are often used in transportation risk analyses to generate accident scenarios and to quantify the frequency of the scenarios. The purpose ofthe event tree is to provide a systematic, logical development of the many potential outcomes of a specific event. The emphasis is on completeness, and the result is often complex. Some accident scenarios will not contribute significantly to the risk result because either the scenario frequency is insignificant, the scenario consequence is insignificant, or both. If the event tree is constructed with completeness as the goal, then many insignificant scenarios will likely be identified. Screening methods can be used to eliminate the insignificant scenarios that have been generated~ however, the analyst will have invested considerable effort to generate a complex tree. Avoiding the generation of insignificant scenarios would be much more cost effective.