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https://nap.nationalacademies.org/catalog/27432/critical-issues-in-transportation-for-2024-and-beyond

Updating RoadHAT: Collision Diagram Builder and HSM Elements

In order to minimize the losses resulting from traffic crashes, Indiana developed its road safety management methods before the Highway Safety Manual (HSM) and the SafetyAnalyst became available. The considerable cost of replacing the Indiana current practice with the safety management based on the Highway Capacity Manual prompted the Indiana Department of Transportation to continue using its own safety management tools. This study includes two related but distinct components: (1) comparison of the HSM-based and Indiana methods of safety management, and (2) development of a Collision Diagram Builder (CDB) to improve current Indiana safety management tools. This study concluded that the HSM safety performance functions (SPFs) would need to be calibrated to the Indiana conditions before they could be used. Calibrating the SPFs for, so-called, base conditions would lead to an insufficient number of roads and, consequently, to estimates that were not trustworthy. This problem is amplified by the large number of road categories and crash types in HSM (110 categories and 468 crash severity proportions). Furthermore, a re-calibration process must be repeated over time to keep the SPFs updated to the changes in safety. An advanced statistical simulation of a safety management system aimed to maximize the total safety benefit was performed. The results indicate that two best performing criteria: the HSM Equivalent Property Damage Only (EPDO)-based criterion and the Indiana total cost of crashes criterion are equivalent and they produce the same results. It is important that the HSM provides guidance as to which screening criteria support which screening objectives because some of the HSM criteria were found inadequate for maximizing the overall safety benefit. It also was concluded that although the cost of crashes and the Index of Crash Cost and Frequency used separately proved to be good screening criteria in Indiana, the combined use of these two measures did not deliver any considerable improvement. Two differences were found between the HSM and Indiana procedures for evaluating the benefits and costs of safety projects: the infinite period of analysis and the road capacity constraint on traffic growth. Consequently, Indiana results depend on the capacity constraints while the HSM results depend on the length of the analysis period. The differences between the two methods were quite limited and they could be fully reconciled if the capacity constraints were relaxed in the Indiana method and a long analysis period assumed in the HSM method. A second major component of the study was to improve the current Indiana safety management tool, RoadHAT2, by developing a computer application facilitating preparation of a so-called collision diagram. These diagrams are an important element of safety audits. They are not used frequently due to a considerable time required to build collision diagrams. The developed application reduces this time from one or two days to an hour or less. The application also provides additional tools for analyzing and visualization of crash patterns. A developed CDB User Manual introduces the user to the tool and provides examples to help the user get familiar with the application.

Language

  • English

Media Info

  • Media Type: Digital/other
  • Edition: Final Report
  • Features: Appendices; Figures; References; Tables;
  • Pagination: 56p

Subject/Index Terms

Filing Info

  • Accession Number: 01618823
  • Record Type: Publication
  • ISBN: 9781622604074
  • Report/Paper Numbers: FHWA/IN/JTRP-2016/11
  • Contract Numbers: SPR-3726
  • Files: NTL, TRIS, ATRI, USDOT, STATEDOT
  • Created Date: Dec 16 2016 11:34AM