The National Academies

NCHRP 22-46 [Active]

Human Factors Guidelines for Road Systems, Proposed 4th Edition

  Project Data
Funds: $550,000
Staff Responsibility: David M. Jared
Research Agency: Exponent
Principal Investigator: John Campbell
Effective Date: 6/1/2021
Completion Date: 9/30/2024



State departments of transportation (DOTs) and other agencies are seeking to implement data-driven, performance-based processes to improve the planning, design, construction, and operation of multimodal transportation systems. Improvements within these project stages require a range of tools to aid understanding of factors contributing to crashes, identification of relevant countermeasures, and implementation of selected solutions. The tools should ensure that all factors related to crashes are considered during project scoping. Historically, the design and operation of road facilities have not adequately accounted for the interaction between road users and the facilities, particularly users who are most vulnerable to crashes. Behavioral factors should be considered by all involved in the planning, design, construction, and operation of multimodal transportation systems.


NCHRP Report 600: Human Factors Guidelines for Road Systems, Second Edition (HFG2), is a tool for integrating road user characteristics into road design and operational decisions. The HFG2 provides human factors (HF) principles and findings for consideration by highway designers, traffic engineers, and other safety practitioners. Since publication of the HFG2, significant research has been completed that adds additional tools and design guidelines for enhancing road user safety. Practitioner needs have developed as well, and research needs have been identified on additional topics, e.g., improving practitioner knowledge of how bicycle and pedestrian behavior at roundabouts affect operations, and the potential impact of these interactions on innovative intersection designs in general. Other potential research topics include aging road users, road diets, complete streets, applying human factors in countermeasure selection, road safety audits, road signage reviews, determination of crash-contributing factors, and root cause analysis. Finally, once research has addressed these topics, training for practitioners on the application of human factors needs to be developed.


NCHRP Project 17-80, “Expansion of Human Factors Guidelines for Road Systems, Second Edition” is currently in progress and addresses HF considerations for bicycle facilities, pedestrian facilities, and roundabouts. This research identified critical gaps in guidelines for considering human factors. It is expected to be published in late 2020 as the Human Factors Guidelines for Road Systems, Third Edition (HFG3).


The HFG, Fourth Edition (HFG4) is intended to supplement the AASHTO Highway Safety Manual (HSM) with other safety tools and processes such as road safety audits, operational reviews, performance planning, and crash data analysis for road system design and operations. Using the “safe systems” approach, roads are designed and operated to reduce the risk of crashes occurring and, if crashes do occur, to reduce the severity of injuries. A safe systems approach seeks to design infrastructures that recognize and accommodate user capabilities for all types of road facilities. HFG4 guidelines will document the best available HF and road/user interaction research and practices in road safety analyses and design to optimize data-driven safety analysis and decision making.





The objective of this research is to prepare a proposed Human Factors Guidelines for Road Systems, Fourth Edition (HFG4), which can be used to by state DOTs and other transportation agencies to integrate HF principles into design and operations across roadway systems for all road users. For this research, road users may include, but not be limited to, drivers, pedestrians, bicyclists, motorcyclists, and electric scooter users.



Task 1. Review existing literature on HF considerations in the design and operations of road systems for all types of road users. Identify a process for scoring relevant literature for its potential inclusion in the HFG4, based on the strength of evidence reported and the literature’s relevance to design and operations from an HF perspective. 

Task 2. Develop a draft survey of practitioners on potential HFG4 content. NCHRP approval of the draft survey is required before work may begin on Task 3. 

Task 3. Survey transportation agencies, professional designers, traffic engineers, planners, HF experts, and others to identify potential HFG4 content. Submit a technical memorandum summarizing the findings of Tasks 1-3. 

Task 4. Recommend (a) adjustments to guidelines from previous HFG editions due to improvements in understanding previously emerging and other technical issues; (b) new technical chapters to be developed, including specific guidelines, with justification for their development; and (c) new print/electronic presentation formats for the HFG4 to increase its usability and its direct cross referencing of other guidance documents such as the HSM, the AASHTO Green Book, the Manual of Uniform Traffic Control Devices (MUTCD), and other widely used resources.

Task 5. Submit an interim report summarizing the findings from Tasks 1-4. A meeting will be held with NCHRP to discuss the interim report. NCHRP approval of the interim report is required before work may begin on Task 6. 

Task 6. Develop updated content for the HFG4 based on Task 4 recommendations approved by NCHRP in Task 5. Outline pilot studies to be conducted in Task 7. Submit a technical memorandum summarizing the findings of Task 6. NCHRP approval of the memorandum is required before work may begin on Task 7. 

Task 7. Conduct at least three pilot studies to (a) clarify proposed analytical approaches and test the components and usability of the methods and tools, in collaboration with transportation professionals on actual projects; and (b) illustrate how multimodal road user safety needs can be addressed using the HFG in combination with other available safety tools. Submit a technical memorandum summarizing the findings of Task 7. NCHRP approval of the memorandum is required before work may begin on Task 8. 

Task 8. Prepare and submit final deliverables to include the following: (a) final report documenting the conduct of research that includes (a) recommendation of needs and priorities for future research and HFG editions; and (b) appendices that list items considered but excluded from the HFG4, with justification of each exclusion; (b) standalone, final version of the HFG4; and (c) training materials to supplement the existing FHWA training course, “Introducing Human Factors in Roadway Design and Operations: A Workshop on How to Use and Apply the Human Factors Guidelines.”

Note: Following receipt of the draft final deliverables, the remaining three (3) months shall be for NCHRP review and comment and for research agency preparation of the final deliverables. 


STATUS: Research is in progress. 


To create a link to this page, use this URL: http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=4778