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Page 16
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2021. Intersection Crash Prediction Methods for the Highway Safety Manual. Washington, DC: The National Academies Press. doi: 10.17226/26153.
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Page 16
Page 17
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2021. Intersection Crash Prediction Methods for the Highway Safety Manual. Washington, DC: The National Academies Press. doi: 10.17226/26153.
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Page 17
Page 18
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2021. Intersection Crash Prediction Methods for the Highway Safety Manual. Washington, DC: The National Academies Press. doi: 10.17226/26153.
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Page 18
Page 19
Suggested Citation:"Summary." National Academies of Sciences, Engineering, and Medicine. 2021. Intersection Crash Prediction Methods for the Highway Safety Manual. Washington, DC: The National Academies Press. doi: 10.17226/26153.
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Page 19

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16 Summary The first edition of the HSM included safety performance functions (SPFs) for roadway segments and intersections. However, not all intersection types are covered in the first edition of the HSM. This research was conducted to develop SPFs for new intersection configurations and traffic control types not covered in the first edition of the HSM, for consideration in the second edition of the HSM. Based on input received through a survey of state and local agencies as well as the research project panel, SPFs were developed for the following general intersection configurations and traffic control types: • Rural and urban all-way stop-controlled intersections • Rural three-leg intersections with signal control • Intersections on high-speed urban and suburban arterials (i.e., roadways with speed limits greater than or equal to 50 mph) • Urban five-leg intersections with signal control • Three-leg intersections where the through movements make turning maneuvers at the intersections • Crossroad ramp terminals at single-point diamond interchanges • Crossroad ramp terminals at tight diamond interchanges The research team coordinated with several state agencies to locate candidate intersections for use in developing the SPFs. Site characteristic data were collected for all candidate intersections to select a final list of sites for model development. In addition, crash and traffic volume data were assembled for model development. The specific intersection configurations and traffic control types and severity levels for which SPFs were developed and recommended for consideration in the second edition of the HSM include: Intersections with All-Way Stop Control • Four-leg all-way stop-controlled intersections on rural two-lane highways - Total crashes • Three-leg all-way stop-controlled intersections on urban and suburban arterials - Fatal-and-injury (FI) crashes - Property-damage-only (PDO) crashes • Four-leg all-way stop-controlled intersections on urban and suburban arterials - FI crashes - PDO crashes

17 Rural Three-Leg Intersections with Signal Control • Three-leg signalized intersections on rural two-lane highways - Total crashes • Three-leg signalized intersections on rural multilane highways - Total crashes - FI crashes Intersections on High-Speed Urban and Suburban Arterials • Three-leg stop-controlled intersections on high-speed urban and suburban arterials - Multiple-vehicle (MV) total crashes - MV FI crashes - MV PDO crashes - Single-vehicle (SV) total crashes - SV FI crashes - SV PDO crashes • Three-leg signalized intersections on high-speed urban and suburban arterials - MV total crashes - MV FI crashes - MV PDO crashes - SV total crashes - SV FI crashes - SV PDO crashes • Four-leg stop-controlled intersections on high-speed urban and suburban arterials - MV total crashes - MV FI crashes - MV PDO crashes - SV total crashes - SV FI crashes - SV PDO crashes • Four-leg signalized intersections on high-speed urban and suburban arterials - MV total crashes - MV FI crashes - MV PDO crashes - SV total crashes - SV FI crashes - SV PDO crashes

18 Five-Leg Intersections with Signal Control • Five-leg signalized intersections on urban and suburban arterials - MV total crashes - MV FI crashes - MV PDO crashes - SV total crashes - SV FI crashes - SV PDO crashes Three-Leg Intersections Where the Through Movement Makes a Turning Maneuver at the Intersection • Three-leg turning intersections on rural two-lane highways - Total crashes • Three-leg turning intersections on urban and suburban arterials - MV total crashes - MV FI crashes - MV PDO crashes - SV total crashes - SV PDO crashes Crossroad Ramp Terminals at Single-Point Diamond Interchanges • Crossroad ramp terminals at single-point diamond interchanges - FI crashes - PDO crashes Crossroad Ramp Terminals at Tight Diamond Interchanges • Crossroad ramp terminals at tight diamond interchanges - FI crashes - PDO crashes In addition to formulating new SPFs, development of SDFs for the new intersection configurations and traffic control types was explored for potential use in combination with the SPFs to estimate crash severity as a function of geometric design elements and traffic control features. However, due to challenges and inconsistencies in developing and interpreting the SDFs, it is recommended for the second edition of the HSM that crash severity for the new intersection configurations and traffic control types be addressed in a manner consistent with existing methods in Chapters 10, 11, and 12 of the first edition of the HSM, without use of SDFs. Draft text recommended for consideration in the second edition of the HSM is provided as an appendix to the report. In addition, the spreadsheet tools developed as part of NCHRP

19 Project 17-38 were updated to incorporate the new intersection crash prediction models developed as part of this research including intersections with all-way stop control, three-leg intersections with signal control on rural highways, intersections on high-speed urban and suburban arterials, five-leg intersections, and three-leg intersections where the through movement makes a turning maneuver at the intersection; and an unlocked version of the Enhanced Interchange Safety Analysis Tool (ISATe) that includes a module for ramp terminals and excludes modules for freeways and ramps was modified to incorporate the new crash prediction models for ramp terminals at single-point diamond interchanges and tight diamond interchanges.

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The first edition of the Highway Safety Manual (HSM), in 2010, included Safety Performance Functions (SPFs) for roadway segments and intersections. However, not all intersection types are covered in the first edition of the HSM.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 297: Intersection Crash Prediction Methods for the Highway Safety Manual develops SPFs for new intersection configurations and traffic control types not covered in the first edition of the HSM, for consideration in the second edition of the HSM.

Supplemental to the Document is recommended draft text for the second edition if the HSM, a worksheet for Chapter 10, a worksheet for Chapter 11, a worksheet for Chapter 12, a worksheet for Chapter 19, and a presentation.

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