Developing Crash-Modification Factors for High-Friction Surface Treatments
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Developing Crash-Modification Factors for High-Friction Surface Treatments

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  • English

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      Final Report
    • Abstract:
      Over the past 10 to 15 yr, the use of high-friction surface treatments (HFSTs) as a safety countermeasure has grown exponentially. HFSTs are pavement-surface treatments that restore or enhance pavement friction at locations with high friction demand, such as curves, ramps, and intersection approaches. While the crash-reduction benefits of HFSTs have been observed by many State highway agencies, the availability of crash-modification factors (CMFs) for HFSTs is limited. This study provides high-quality and robust CMFs and benefit–cost ratios for HFSTs with calcined bauxite aggregate and recommends materials and specifications (as appropriate) for applications. This study also notes where and under what conditions to use HFSTs to effectively reduce roadway-departure crashes. This study was data-driven and used before- and after-crash data to quantify crash-reduction benefits. The study also used friction data collected by the research team before (when available) and after HFST installation to help quantify the impact of increased pavement friction on the CMFs. Data were collected for hundreds of HFST installations in Arkansas, Georgia, Kentucky, Louisiana, Pennsylvania, and West Virginia on curves and ramps. The results for curves and ramps indicate significant benefits in terms of low CMFs, particularly for wet-weather crashes. A thorough disaggregate analysis of the before–after evaluation data for curves suggested a logical and consistent relationship between CMFs and three variables: friction improvement, annual average daily traffic, and expected crash frequency before treatment. A complementary evaluation was conducted under this study for friction changes of HFSTs over time; the results are documented in FHWA-HRT-20-062, Developing Crash-Modification Factors for High-Friction Surface Treatments: Friction Change Report. Friction testing was performed on several older HFST installations where previous friction data were collected. All friction testing was performed with the Federal Highway Administration’s highway friction tester, a continuous fixed-slip measurement device. The friction data collected during this research and documented in this report were evaluated for friction change before and after HFST installation, friction change of the HFST and existing pavement over time, and friction change through a curve.
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