American Association of State Highway and Transportation Officials

Special Committee on Research and Innovation

FY2023 NCHRP PROBLEM STATEMENT TEMPLATE

Problem Number: 2023-G-09

Problem Title

Practical Approaches to Quantifying Safe System Concepts

Background Information And Need For Research

For 2020, according to the National Highway Traffic Safety Administration (NHTSA), estimates show that 38,680 people died in motor vehicle traffic crashes. This represents the largest projected number of fatalities since 2007. This figure represents an increase of about 7.2 percent as compared to the 36,096 fatalities reported in 2019. These figures demonstrate that traffic-related deaths continue to be a serious public health issue.

Worldwide, the use of Safe System principles for roadway design and operations is showing significant success in driving down fatal and serious crashes for all road users, including those who walk and bike. The Safe System approach recognizes that all road users should be treated equitably, in a manner that considers safety tradeoffs for all, and that death and serious injury are preventable when consideration is given to the tolerance of the human body to crash forces. In addition, the Safe System approach applies to all roadways: urban or rural, and under state, local or tribal jurisdiction. The Safe System approach recognizes that human errors occur and that by designing and operating road infrastructure to account for these errors crash likelihood is reduced.

This research directly supports the AASHTO Committee on Safety’s Strategic Plan goal to “partner in the implementation of a national highway safety strategy and performance measures to reduce fatalities and serious injuries on all public roads and locations where roads intersect with other modes of transportation." In addition, the strategic goals to “institutionalize analytical tools to advance the science of safety” and “provide data-driven safety technical and policy advice” are supported by this research.

Literature Search Summary

This research will provide specific applications to advance the Federal Highway Administration (FHWA) published “Integrating the Safe System Approach with the Highway Safety Improvement Program: An Informational Guide”. The FHWA publication “A Safe System-Based Framework and Analytical Methodology for Assessing Intersections” outlines a set of future research steps that are in line with the objectives of this research. In addition, this research will complement the NCHRP 17-101 project “Safe System in the U.S.: Developing a Roadmap for Transportation Road Designers, Planners, and Engineers” as a first step in Safe System implementation in the United States. This research will provide applications that build upon the practices highlighted in The Institute of Transportation Engineers (ITE) document "Case Studies on Implementing the Safe System Approach in the U.S.”

Research Objective

The objective of this research is to investigate the correlation between a Safe System for Intersections (SSI) score and observed fatal and serious injury crash frequency at an intersection so that a benefit/cost ratio or cost effectiveness associated with the SSI score can be determined. This methodology can then be applied to corresponding roadway segments. The research will also recommend how the SSI can be adopted to design and operational criteria for future implementation. Pilot testing of the research results will be used to validate and strengthen the methodology and will provide additional knowledge to those transportation agencies implementing the new model.

The Safe System approach applies to all roadways, urban and rural, and relies on analysis and evaluating/quantifying the safety benefits of differing design and operational alternatives. Importantly, the FHWA SSI report (FHWA-SA-21-008) provides a method for developing a SSI score and other Safe System related metrics that quantify exposure, complexity, and severity in the event of different crash types. This method also provides for an assessment of a wide selection of intersections, including but not limited to signalized urban intersections and rural uncontrolled intersections. This SSI method can be applied at a project level and be incorporated into an Intersection Control Evaluation (ICE) alternatives screening process to provide another metric for safety. While a compilation of states’ existing activities may be beneficial, new research is needed to assess the significance of the correlation of the Safe System approach and the SSI method currently underway in several states. For example, Florida DOT is in the process of adding SSI into the Safety Performance for Intersection Control Evaluation (SPICE) spreadsheet and will be effective January 2022. The SSI analysis will be for all intersection forms included in the FDOT SPICE. The FDOT ICE Manual is also being revised to discuss the SSI analysis compared to the SPF crash prediction. Massachusetts used the SSI approach to compare design alternatives for intersection types that do not have Safety Performance Functions.

This SSI process still requires several high-level assumptions to be included in the analysis that impact the outcome and states are reluctant to adopt these assumptions without some level of validation. The method is a combination of quantitative concepts (such as exposure and fatal and serious injury probability) and qualitative concepts (such as user complexity and comfort).

Major activities:

a. Further test the SSI approach so that efforts can be made to validate and calibrate the SSI method with crash data at differing crash severity level, differing urban and rural locations, and develop a means to compare the output of the SSI models with actual safety performance at existing locations to better integrate these methods into the Safety Management Process. This will support the use of the SSI approach for alternative analysis, prioritization of projects and with implementing effective projects as part of a successful Highway Safety Improvement Program (HSIP).

a. Develop refined input SSI criteria, including pedestrians and bicyclist paths through intersections, to improve upon the high-level assumptions and enhance the selection of intersection crash types (ex: rear end crashes) and intersection geometric inputs such as turn lanes. This will provide more realistic and usable results for transportation agencies at all levels.

b. Use the initial research findings to conduct pilot testing of the SSI model in volunteer states and assess the research findings.

c. Expand the quantification of the Safe Systems approach to cover segments and to use existing crash data to estimate the kinetic energy models for those segments.

d. Development of dissemination materials for use by transportation agencies in the use and implementation of the SSI, including items such as worksheets, analysis tools and presentations.

Research results should be presented in a final report and guidance that gives clear and actionable strategies to state DOTs and other agencies to effectively implement safe system principles.

Urgency And Potential Benefits

Searching For Opportunities To Reverse the upward trend in traffic fatalities, many States are interested in moving towards a Safe System approach and have been looking at practical ways to reduce crash forces at intersections and roadways. In some cases, this has resulted in the development of policy changes in speed management and design directives.

According to FHWA guidance, there are six principles that form the basis of the Safe System approach: deaths and injuries are unacceptable, humans make mistakes, humans are vulnerable, responsibility is shared, safety is proactive, and redundancy is crucial. Road design and operation seeks to reduce complexity and to manage speeds and crash angles so that all road crashes and severity of those crashes are lowered. Without this research, advancement in a practical data-driven application of the Safe System approach could be limited.

This research will help safety professionals more fully understand the relationships between economic, regulatory, vehicle, and infrastructure factors and traffic fatalities and the mechanisms by which they operate to provide states with insights that can be used to target fatality reduction programs and projects. Moreover, strategies that combine domains will be important for using state resources efficiently to maximize fatality reductions.

This research tied for top priority for the AASHTO Committee on Safety.

Implementation Considerations

There are several potential users of this research, namely state DOT traffic and safety engineers as well as State Governor’s offices of Highway Safety and local agencies. The states of Florida, Massachusetts and Virginia have already used the SSI approach to enhance their respective safety performance initiatives. The research could have direct application to state implementation of the HSIP, enhanced safety performance target development, and future safety funding requests. The results of the research could be disseminated through technical presentations and peer exchanges. Pilot testing of the SSI model would strengthen the overall research and benefit future implementation. The AASHTO Committee on Safety is interested in this research and will assist the member states with implementation. Also, the FHWA Office of Safety is interested in this research.

Recommended Research Funding And Research Period

Research Funding: A proposed budget of $450,000 would be necessary to complete the research tasks, the pilot testing, and training via a webinar or through a peer exchange

Research Period: The expected time-period to complete the research is 24 months including the pilot testing and the webinar/peer exchange.

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

Bonnie Polin

Massachusetts Department of Transportation

617-365-5700

Bonnie.Polin@state.ma.us

John Milton

Washington State Department of Transportation

360-791-9242

MiltonJ@wsdot.wa.gov

Robert E. Hull, P.E., RSP2I

Robert Hull Transportation Safety

801-633-6400

robert@roberthulltransportationsafety.com

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

Bonnie Polin

Massachusetts Department of Transportation

AASHTO Committee on Safety

617-365-5700

Bonnie.Polin@state.ma.us

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