What Is the Role of Multiple Secondary Incidents in Traffic Operations?

Traffic incidents are a major source of travel uncertainty, imposing substantial costs on the transportation system. Sometimes, an incident can result in one or more secondary incidents, which can be particularly problematic. To identify roadways where multiple secondary incidents are more likely to occur and analyze primary and secondary incidents, an innovative analysis method based on a detailed incident data set from Hampton Roads, Virginia was developed. Incidents occurring on major freeways are categorized on a three-point ordinal scale as (1) an independent incident, i.e., an incident not associated with any secondary incidents; (2) one primary-secondary pair; and (3) one primary with two or more secondary incidents in the same or opposite directions. This scale captures event adversity from a traffic management perspective, with the last category capturing multiple secondary events. To quantify associations with key factors that include incident characteristics, roadway geometry and traffic flow, ordinal regression models are estimated. The results indicate that longer duration crashes, shorter segments, and heavy traffic are associated with higher propensity for secondary incidents. Furthermore, multiple-vehicle involvement and lane blockage are associated with multiple secondary incidents. The findings provide engineers and planners with valuable information on targeting service patrols in areas that are more prone to multiple secondary incidents. Overall, this research contributes by characterizing and analyzing complex events involving secondary incidents using rigorous statistical methods.