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Identifying Primary and Secondary Crashes from Spatiotemporal Crash Impact Analysis

The identification of secondary crashes is accompanied by the definition of the primary crash impact area. Although the crash impact area varies with the geometric characteristics of roads and periodic characteristics of traffic flow as well as with crash type, most previous studies have used a fixed boundary to identify secondary crashes and primary crashes. Thus, the objective of this research is to develop a method to define the spatiotemporally different boundaries varying with different types of crash. On the basis of the developed boundaries, the secondary crash is identified in the primary crash location as well as in its opposite direction. Secondary crashes in the same and opposite directions are identified to be 7.4% and 3.8% of total primary crashes, respectively. Also, only 0.3% of total primary crashes are connected with the secondary crash in both the same and the opposite directions. Although the proposed method seems to be complicated, the results will be useful in understanding secondary crash characteristics in a more realistic analysis through the spatiotemporal crash impact area in the crash direction as well as in the opposite direction. Specifically, the results can be used by public-sector transportation agencies in making operational strategies for reducing secondary crashes on freeways.