Statistical and Queuing Analyses of Freeway Incidents in Washington State

Freeway incidents cause major traffic operational problems in the State of Washington. In order to alleviate the severity of incident-induced congestion, a better understanding of incident causes, features, and impacts is indispensable. To accomplish this goal, extensive incident data from the Washington state incident tracking system (WITS) database were statistically analyzed. The queuing analysis, by the use of archived loop detector data, was also applied to evaluate the possible incident impacts on traffic flow during incident duration. Incorporating the statistical and queuing analyses help identify the main categories of incidents on Washington state´s freeways and the relationships between incident parameters and incident impacts on freeway traffic. Benefits of reducing incident response times and incident clear times were also discussed based on the queue length information. The analysis results can be applied as the guidance for an incident response team to select most effective countermeasures against incident-induced congestion.