The Highway Safety Manual (HSM) provides comprehensive screening methodologies for microscopic entities such as segments, intersections, or corridors (AASHTO, 2010). While microscopic screening analysis can identify specific locations with high traffic crash risk, macroscopic screening investigation can consider an overall zonal level risk. In Phase I of the project, we followed the HSM screening procedure and extended it to the macroscopic level. Thus, our vision is to provide more practical and useful safety screening methodologies with comprehensive and balanced perspectives, macro- and micro-levels. TAZs (Traffic analysis zones) have been most widely used as a spatial unit for macroscopic analysis; however, TAZs have two disadvantages: small size in urban areas and high percentage of zonal boundary crashes. Thus, in this study we have suggested two ways to overcome this issue. The first way is to develop a new study unit — Traffic safety analysis zones (TSAZs) by aggregating existing TAZs with similar crash rates. The second way is to apply a larger geographic unit such as TADs (Traffic analysis districts) or counties. We explored traffic safety not only at TAZs but also at TSAZs, TADs, and counties. The research team developed Florida-specific SPFs (Safety performance functions) both at the macro-level and micro-level for 17 crash types. At the macro-level, overall, 204 SPFs were developed based on SWTAZs (Statewide TAZs), TSAZs, TADs, and counties. The research team has found various contributing factors for each traffic crash type at the macro-level. At the micro-level, overall, 404 SPFs were estimated for 13 segments and 16 intersection facility types. Before the research team proceeded to the screening analysis, we performed a grid structure analysis to identify the best geographic units. The results showed that SWTAZs are the optimal zone system for screening non-motorized crashes such as pedestrian and bicycle crashes. On the other hand, TADs are found to be the best geographic unit for all other crash types. Subsequently, screening analysis was conducted at the two-levels using PSI (Potential for Safety Improvement) and ranked. The screening results from the two levels were integrated, and all the results were provided in Excel spreadsheets for the convenient application for practitioners. In summary, this project developed numerous Florida-specific SPFs both at macro-level and micro-level using statewide data. The research team explored 17 major crash types. The research team suggests using TADs as a geographic unit along with SWTAZs, TSAZs, and counties. Moreover, this project presents a separate and an integrated screening method that can be used to overcome the shortcomings of macro- and micro-level approaches by integrating the two levels. A reasonable approach is two steps: first identify the problematic areas; second zoom in with micro-screening to identify the specific problems and locations. It is intended that the results of the project would provide a comprehensive perspective on appropriate traffic safety plans and help practitioners screen and rank any area, segment, or intersection in the state. (Author/publisher)
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