Primary and Secondary Incidents: Management Strategies

The overall objective of the study is to understand the occurrence of primary and secondary incidents and relevant incident management strategies, as well as to understand how primary incident duration and secondary incident occurrence are related. Specifically, secondary incidents are more likely to occur if the primary incident lasts long; at the same time, the durations of primary incidents are expected to be longer if secondary incidents occur. The work will allow State Departments of Transportation to estimate the chances of a secondary incident based on the characteristics of the primary incident, evaluate associated delays, and aid in identifying incident management strategies to mitigate the impacts of both primary and secondary incidents. Freeway incident and roadway inventory data from the Hampton Roads area in Virginia were used in this study. Modeling and simulation techniques were applied to develop primary incident duration and secondary incident occurrence/duration prediction models. Models for primary incident durations and whether or not a secondary incident occurs are estimated. The interdependence is modeled by using the incident duration as endogenous variable in secondary incident occurrence models. The results show statistical evidence for interdependence, but when it is taken into account, no substantial differences in the magnitudes and statistical significance for the estimated independent variables are found (compared to when the interdependence is not accounted for). Statistically significant correlations are found between secondary incident occurrence and other variables, allowing us to recommend aggressive incident clearance procedures on qualifying high-volume roadways to avoid secondary incidents.