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210 Chapter 10. Conclusions and Recommendations The following conclusions and recommendations have been developed in this research: 1. The SPFs presented in this report have been developed consistent with existing methods in HSM Part C and comprehensive in their ability to address a wide range of intersection configurations and traffic control types in rural, urban, and suburban areas. The SPFs recommended for inclusion 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 - FI crashes - PDO crashes ⢠Four-leg all-way stop-controlled intersections on urban and suburban arterials - FI crashes - PDO crashes 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 - MV total crashes - MV FI crashes - MV PDO crashes - 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
211 ⢠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 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
212 Crossroad Ramp Terminals at Tight Diamond Interchanges ⢠Crossroad ramp terminals at tight diamond interchanges - FI crashes - PDO crashes Recommended draft text for inclusion in the second edition of the HSM is presented in Appendix A that incorporates the new crash prediction models for the intersection configurations and traffic control types developed as part of this research. 2. Development of SDFs for most of 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. 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. Future research should continue to explore the most promising approaches for addressing crash severity in the HSM predictive methods. 3. Crash prediction models could be developed for additional intersection configurations and traffic control types that are not addressed in the first edition of the HSM and were not developed as part of this research. For example, several additional intersection configurations and traffic control types for which crash prediction models could be developed include: ⢠Three-leg intersections with a commercial driveway forming a fourth leg ⢠Intersections with indirect left turns from the minor road (e.g., U-turns or J-turns) ⢠Intersections with yield or no control ⢠Rural five-leg intersections ⢠Urban and suburban five-leg intersections with minor road stop control ⢠Six-or-more-leg intersections ⢠Diverging-diamond ramp terminals 4. Future research should be conducted to further evaluate approaches to defining boundaries of an intersection for purposes of assigning crashes to the intersection for model development. Especially for intersection configurations that have a large footprint such as the crossroad ramp terminal at a single-point diamond interchange and some of the new alternative intersection configurations (e.g., diverging-diamond ramp terminals), a consistent approach for assigning crashes to intersections for crash prediction and comparison of alternative intersection configurations is necessary.
