Implementing Self-Explaining and Self-Enforcing Roads

It is often stated that approximately 95% of crashes are related to human behavior. While the exact percentage is debated, most crashes involve human factors, highlighting the limits of treating crashes solely as driver failings rather than as predictable interactions between people and the road environment. There are clear opportunities to address human factors and behavior throughout the planning, design, and operation of roadway networks. The Safe System Approach (SSA) encourages agencies to reframe safety by designing systems that anticipate human limitations and ensure that inevitable mistakes do not lead to fatal outcomes. Making that approach routine requires changes to both the physical roadway and agency procedures, so that networks better align with how people perceive, decide, and act. Human-factors research shows how roadway geometry, visual clutter, inconsistent signing, unexpected transitions, and operational variability increase cognitive load and the likelihood of errors. Human-factors research also identifies countermeasures that improve expectancy, reduce task demand, and encourage compliance. Despite this evidence and existing guidance, implementation barriers remain. Design manuals and operational policies often emphasize mobility, capacity, or legacy practice over behavioral predictability, and research recommendations are not always framed in language agencies can adopt as policy. This gap slows adoption of treatments that would make roads more self-explaining—where users immediately understand how to behave—and self-enforcing—where the environment naturally limits unsafe choices. Agencies, therefore, need a practical bridge from science to policy and routine practice to implement SSA principles at scale. OBJECTIVE: The objective of this research is to develop a guide and draft sample policies that enable transportation agencies to operationalize human-factors principles through roadway design and operations manuals and policies. This work will translate existing human-factors research into clearly written, implementable edits for design and operations manuals; illustrate practice-ready examples across facility types; and identify pragmatic changes to agency business processes and policies to support adoption.

• Record URL:
  • http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=6061
• Supplemental Notes:
  • Contract to a Performing Organization has not yet been awarded.

Language

• English

Project

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

  Project 20-144

• Sponsor Organizations:

  National Cooperative Highway Research Program

  Transportation Research Board
  500 Fifth Street, NW
  Washington, DC  United States  20001

  American Association of State Highway and 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
• Project Managers:

  Turner, Anne-Marie

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

Subject/Index Terms

• TRT Terms: Highway design; Highway operations; Highway safety; Human factors
• Identifier Terms: Safe System Approach
• Subject Areas: Design; Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01992136
• Record Type: Research project
• Source Agency: Transportation Research Board
• Contract Numbers: Project 20-144
• Files: TRB, RIP
• Created Date: Jun 9 2026 12:41PM