Safety Performance of Safe System Treatments for Corridors and Intersections that May Impact Capacity

Transportation agencies are increasingly adopting the Safe System Approach (SSA), which emphasizes a holistic approach to eliminating all fatal and serious traffic injuries on road segments and at intersections. Historically, efforts to reduce congestion often led to the addition of through lanes, implementation of short auxiliary lanes at intersections to facilitate right turns and through movements, and other treatments. However, agencies are now exploring lane reductions—commonly referred to as right-of-way reallocation, road diets, or reconfigurations—to improve safety. In some cases, roads previously widened to accommodate peak-hour traffic are being reevaluated through the lens of the SSA. Implementing these changes requires a comprehensive understanding of the associated safety impacts and the ability to predict crash outcomes resulting from modifications to roadway capacity. Safety outcomes associated with capacity modifications carry substantial weight in routine planning and operational decisions. Current evidence, however, is limited, and context specific effects, especially for vulnerable road users, are not well quantified. Additional research is therefore needed to quantify how short auxiliary lanes and cross-section changes affect exposure, likelihood, and severity. The objectives of this research are to (1) quantify the safety impacts of SSA treatments that may affect roadway capacity and (2) develop analysis methodologies, such as crash modification factors (CMFs) and crash prediction models, to evaluate how these treatments affect crash exposure, likelihood, and severity across all road users and crash types. The research results can enable planners, designers, traffic engineers, and other decision-makers to make evidence-based choices that balance safety with operational and capacity needs. Potential research tasks include: Developing a practitioners’ guide that summarizes analysis methodologies and includes descriptions and examples of their application; Developing a series of one- to two-page briefing documents describing the safety benefits and potential capacity impacts of the SSA treatment researched in this project; Conducting a virtual workshop with state departments of transportation safety practitioners to review draft briefing documents and the draft practitioners’ guide.

• Record URL:
  • http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=6052
• Supplemental Notes:
  • Contract to a Performing Organization has not yet been awarded.

Language

• English

Project

• Status: Proposed
• Funding: $600,000.00
• Contract Numbers:

  Project 17-147

• Sponsor Organizations:

  State Departments of Transportation (participating member states of American Association of State Highway Transportation Officials (AASHTO))

  American Association of State Highway Transportation Officials (AASHTO)
  444 North Capitol Street, NW
  Washington, DC  United States  20001

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Managing Organizations:

  National Cooperative Highway Research Program (NCHRP)

  Transportation Research Board
  500 Fifth Street, NW
  Washington, DC  United States  20001
• Project Managers:

  Zelinski, Patrick

• Start Date: 20261001
• Expected Completion Date: 0
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Crash risk forecasting; Highway capacity; Highway design; Highway safety; Intersections
• Identifier Terms: Safe System Approach
• Subject Areas: Design; Highways; Planning and Forecasting; Safety and Human Factors;

Filing Info

• Accession Number: 01992185
• Record Type: Research project
• Source Agency: Transportation Research Board
• Contract Numbers: Project 17-147
• Files: TRB, RIP
• Created Date: Jun 9 2026 3:00PM