Existing Conditions
2.5 Collision Mapping Overview
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Figure 2-8: High-Injury Network Method
Understanding the roadway conditions where severe-injury and fatal collisions occur is fundamental to addressing unsafe conditions in other places before these types of collisions occur. Mapping what is known as the “high-injury network” identifies segments of roadway that have been the location of the highest number of pedestrian-involved, bicyclist-involved, severe-injury or fatal collisions. By learning the characteristics of high-injury road segments, these conditions can be remedied citywide where clusters of collisions occur. A “collision tree” grouping method helps identify clusters of collisions that occur in the same conditions as the high-injury network. Collision mapping was performed in the following two ways: 1. A high-injury network method that ranks road segments by weighting the collisions that occurred on each segment over the study period 2. A collision tree method that groups and maps collisions by the roadway conditions where they occurred.
2.5.1 High-Injury Network The high-injury network (HIN) method identifies segments of roads with concentrations of fatal and severe injury (Killed or Significantly Injured-KSI) collisions. The goal of this method is to identify connected segments of roadway with a high number of collisions that together form a high-injury corridor where safety improvements can be implemented. With this method, bicyclist-involved and pedestrian-involved collisions are weighted 25% more than auto-only collisions. Fatal auto-only collisions are also weighted 25% more than non-fatal collisions. Figure 2-8 shows the process for identifying high-injury seg�ments. For both methods, larger sums indicate more collisions, or a sum of relatively fewer auto-only collisions combined with bicycle- or pedestrian-involved collisions on the same road segment.
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