Calibration of HSM Predictive Methods on State and Local Rural Highways

Performance-based safety goals and objectives are more attainable with the use of the Highway Safety Manual (HSM). However, the safety performance functions (SPFs) in the HSM are not accurate because they are not calibrated to local conditions. Additionally, each SPF and crash modification factor (CMF) assumes a set of base site conditions which might not be realistic or representative of local roadways. The calibration procedures provided in HSM Part C Appendix A should therefore be modified to accommodate local data availability as well as roadway, traffic, and crash characteristics. Furthermore, a set of base conditions applicable to local highways should be determined. This study presents the application of the HSM to rural state highways in South Dakota and provides important guidance and empirical results regarding how to calibrate HSM models. Calibration guidelines have been developed to facilitate future calibration activities. The calibration was based on crash data from three roadway segment types and five highway intersection types during a five-year period (2008-2012). The calibration process includes establishing new base conditions, developing SPFs, converting CMFs to base conditions, and deriving calibration factors. Considering the sample size, base conditions, and prediction accuracy, four state-specific SPF models have been developed for two segment types (two-way two-lane and multilane divided) and two intersection types (two-way two-lane three-leg STOP and two-way two-lane four-leg STOP), respectively. The HSM SPFs are retained for other highway facility types. The values of calibration factors for crashes are derived by injury severity scale (i.e., killed, type A, B, or C injury, and property-damage-only crashes). Results show that the number of crashes observed in South Dakota can be drastically different from those predicted by the HSM. The HSM models in this study underestimate the total crash count on roadway segments for all rural state highway segment types in South Dakota. On the other hand, the models overestimate the total crash count at intersections for all the intersection types in South Dakota except multilane three-leg STOP sites. The HSM models overestimate fatal and injury crashes in all highway facility types. Property-damage-only crashes are sometimes overestimated by 200% and sometimes underestimated by 72%. The state-specific SPF models developed from South Dakota’s safety data perform better for facility types that are not adequately predicted by the HSM method. The recommendation is to use a hybrid method with both HSM and state-specific models for certain segment and intersection types to achieve high crash prediction accuracy.

• Record URL:
  https://www.ugpti.org/resources/reports/details.php?id=992
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/70411
• Supplemental Notes:
  • This document was sponsored by the U.S. Department of Transportation, University Transportation Centers Program. Cover date: August 2020.
• Corporate Authors:

  University of Wisconsin, Madison

  Department of Civil and Environmental Engineering
  1415 Engineering Drive
  Madison, WI  United States  53706

  South Dakota Department of Transportation

  700 East Broadway Avenue
  Pierre, SD  United States  57501

  Mountain-Plains Consortium

  North Dakota State University
  Fargo, ND  United States  58108

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590

  Office of the Assistant Secretary for Research and Technology

  University Transportation Centers Program
  Department of Transportation
  Washington, DC  United States  20590
• Authors:
  • Qin, Xiao
  • Chen, Zhi
  • Shaon, Mohammad Razuar
• Publication Date: 2020-6-30

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Final Report
• Features: Appendices; Figures; Maps; References; Tables;
• Pagination: 90p

Subject/Index Terms

• TRT Terms: Calibration; Crash modification factors; Injury severity; Rural highways
• Identifier Terms: Highway Safety Manual; Safety Performance Functions
• Geographic Terms: South Dakota
• Subject Areas: Highways; Safety and Human Factors;

Filing Info

• Accession Number: 01751955
• Record Type: Publication
• Report/Paper Numbers: MPC-20-416, SD2013-04-F
• Contract Numbers: MPC-438; 311179
• Files: UTC, NTL, TRIS, ATRI, USDOT, STATEDOT
• Created Date: Sep 17 2020 5:51PM