Reducing Secondary Crashes through Effective Traffic Incident Management

Currently on its crash form, Arizona is the only state that is recording incident data on the three Traffic Incident Management (TIM) performance measures for collection and analysis: (1) Roadway Clearance Time: This interval is defined as the time between the first recordable awareness of an incident (detection, notification, or verification) by a responding agency and first confirmation that all lanes are available for traffic flow. (2) Incident Clearance Time: This interval is defined as the time between the first recordable awareness of the incident and the time at which the last responder has left the scene. (from FHWA-HOP-10-013 "Traffic Incident Management Handbook") (3) Secondary Crashes: The number of secondary crashes beginning with the time of detection of the primary incident where a collision occurs either a) within the incident scene or b) within the queue, including the opposite direction, resulting from the original incident. According to Zhan et al., secondary crashes are generally defined as crashes that occur as a result of primary incidents. They go on to state that "there is no uniform definition of a secondary crash in terms of its spatial and temporal relationship to the primary incident…it has been difficult to associate an initial incident with secondary crashes and to confirm that the first incident was indeed a contributor to the subsequent crashes." For the purposes of this research, a secondary crash is defined as a crash resulting directly from any primary roadway incident (see the third bullet above). Depending on the nature of the reporting by the official, a secondary crash may or may not be difficult to define or determine. It is expected that the three TIM performance measures are somehow interrelated or can be correlated with each other to provide a clearer understanding of these highly complex phenomena. "Roadway Clearance Time" and "Incident Clearance Time" are the two TIM components that can be associated with the incident management of a primary crash. Reduction of the "Secondary Crashes" component is what this research will attempt to assess by looking at the incident management that leads to the first two performance measures.