Enhancing and generalizing the two-level screening approach incorporating the Highway Safety Manual (HSM) methods, phase 2.
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2016-04-01
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Edition:Final Deliverable (Draft)
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Abstract:This project aims at developing a novel methodology to identify traffic safety hotspots and hot zones for at the macroscopic
and microscopic levels. In order to achieve these objectives, the following tasks were performed. The research team
followed the HSM screening procedure and extended it to the macroscopic level. 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, we have suggested two ways to overcome this issue. The first
way is to develop a new study unit – Traffic safety analysis zones (TSAZs), created 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 for TAZs only but also for TSAZs, TADs, and counties. The research team developed a series
of 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 Floridaspecific
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 analyzing 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. Two stage screening could be
suggested as a simple way to identify high risk locations. The screening results from the two-levels were integrated, and all
the results were provided in Excel spreadsheets for the convenient application of practitioners. 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.
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