American Association of State Highway and Transportation Officials

Special Committee on Research and Innovation

FY2023 NCHRP PROBLEM STATEMENT TEMPLATE

PROBLEM NUMBER: 2023-G-06

Problem Title

Intersection Crash Prediction Models for Future Editions of the HSM

Background Information And Need For Research

In 2010, AASHTO published the first edition of the Highway Safety Manual (HSM). HSM Part C includes methods to predict the safety performance of new facilities, assess the safety performance of existing facilities, and estimate the expected effectiveness of proposed improvements to existing facilities. In preparing the first edition of the HSM, decisions that determined which facility types would be addressed by the predictive methods chapters were made based on availability of data, funding limitations, and highway agency priorities. Since the preparation and publication of the first edition of the HSM, several NCHRP projects have been funded to expand the safety knowledge and improve the crash prediction methods provided in Part C of the first edition of the HSM.

The HSM Part C provides the capability to analyze the safety performance of approximately thirteen intersection configurations and traffic control types as shown in Table 1.

Table 1. Intersection types addressed by predictive methods in the first edition of the HSM

Intersection Type	HSM Chapter
	10	11	12	19
Three-leg intersections with stop control on minor approach	X	X	X
Four-leg intersections with stop control on minor approaches	X	X	X
Three-leg intersections with signal control			X
Four-leg intersections with signal control	X	X	X
Diamond ramp terminals at crossroad				X
Parclo ramp terminals at crossroad				X
Free-flow ramp terminals at crossroad				X

Recently, research was conducted to develop crash prediction methods for intersection configurations and traffic control types not covered in the first edition of the HSM. In NCHRP Project 17-68, crash prediction methods were developed for the following general intersection configurations and traffic control types for consideration in the second edition of the HSM (currently being produced under NCHRP Project 17-71A):

• 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

To further expand the intersection types addressed in future editions of the HSM (i.e., HSM3), 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 for HSM2 as part of NCHRP Project 17-68. For example, several additional intersection configurations and traffic control types for which crash prediction models could be developed for future editions of the HSM include:

• Intersections with frontage roads

• Restricted crossing U-turn intersections (RCUTs)

• Median U-turn intersections (MCUTs)

• Jughandle intersections

• Displaced left-turn intersections

• Continuous green tee intersections

• 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

The need for this research is based on the results of NCHRP Project 17-68 and a clear understanding of what is planned for incorporation in the second edition of the AASHTO Highway Safety Manual. Thus, the recommended scope for this research, as stated above, is appropriate for further research beyond the second edition of the HSM.

Literature Search Summary

A review of previous studies that addressed the safety performance of intersections was conducted. The final report from NCHRP Project 17-68 provides a detailed summary of the intersection safety performance functions (SPFs) and crash prediction models (CPMs) included in the first edition of the HSM and planned for incorporation in HSM2. Several other studies have documented the safety performance of intersection types that will not be addressed in the HSM2; but these studies address the general safety performance of these intersections and/or provide estimated crash modification factors (CMFs) for these intersections. For these other intersection types not addressed in the HSM, CPMs need to be developed in a consistent manner with procedures in the HSM so that comparisons can be made about the relative safety performance of different intersection configurations and traffic control types.

Research Objective

The objective of this research is to develop new intersection crash prediction models (CPMs), as discussed above, for potential inclusion in a future edition of the HSM that are 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 and urban areas. The new CPMs should be developed so that comparisons can be made between the safety performance of intersection types included in the HSM and the intersection types that will be addressed in this research.

Urgency and Potential Benefits

Intersections create conflict points where crashes can occur. Annually, approximately 28 percent of traffic fatalities in the United States occur at intersections. State and local transportation agencies across the United States are looking for ways to reduce the frequency of crashes, particularly fatal and serious injury crashes, at intersections. This research will help agencies assess the safety performance of intersections under their jurisdiction and help to evaluate the safety performance of design alternatives that may be considered either to improve the safety performance of existing intersections or when designing new intersections.

The research was ranked priority #8 by the AASHTO Committee on Safety.

Implementation Considerations

State and local transportation agencies and safety practitioners are looking for guidance and tools to evaluate the safety performance of a range of intersection configurations and traffic control types to help them make more educated decisions. This research is intended to expand the range of intersection configurations and traffic control types for which quantitative safety performance estimates can be made to aid with the decision-making process.

Recommended Research Funding and Research Period

The funds and time period necessary to accomplish the research objectives are estimated to be $750,000 over a 30-month period of performance.

Problem Statement Author(S): For each author, provide their name, affiliation, email address and phone.

Darren J. Torbic, Ph. D.

Research Scientist

Texas A&M Transportation Institute

Email: d-torbic@tti.tamu.edu

Phone: (814) 574-9194

Potential Panel Members: For each panel member, provide their name, affiliation, email address and phone.

John Milton, Washington State DOT, miltonj@wsdot.wa.gov, 360-704-6363

Derek Troyer, Ohio DOT, derek.troyer@dot.state.oh.us, 614-387-5164

Jason Hershock, Pennsylvania DOT, jhershock@pa.gov, 717-783-8012

Dennis Emidy, Maine DOT, dennis.emidy@maine.gov, 207-624-3309

Michael Vaughn, Kentucky Transportation Cabinet, mike.vaughn@ky.gov, 502-782-4923

Jeff Shaw, FHWA, Jeffrey.shaw@dot.gov, 202-738-7793

Jerry Roche, FHWA, jerry.roche@dot.gov, 515-233-7323

Person Submitting The Problem Statement: Name, affiliation, email address and phone.

Adnan Qazi, P.E.

Arkansas Department of Transportation

AASHTO Committee on Safety, Research Subcommittee Chair

501-569-2642

Adnan.Qazi@ardot.gov