1.0 Introduction

A number of existing guides, standards, and references are available to facilitate safe roadway design and operational decisions, including the American Association of State Highway and Transportation Officials (AASHTO) Green Book, the Manual on Uniform Traffic Control Devices (MUTCD), and the Highway Safety Manual (HSM). However, these materials often lack a substantive presentation and discussion of Human Factors principles and concepts that could be used by highway designers and traffic engineers to improve roadway design and traffic safety. Despite a widespread acknowledgement that traffic safety reflects the consideration and integration of three components—the roadway user, the vehicle, and the roadway environment—the information needs, limitations, and capabilities of roadway users are often neglected in traditional resources used by practitioners. In short, existing references applicable to road system design have limitations in providing planners, highway designers, operations staff, and traffic engineers with adequate guidance for incorporating road user needs, limitations, and capabilities when dealing with design and operational issues.

In response to this need, the National Cooperative Highway Research Program (NCHRP) initiated a series of projects to develop a new resource document for highway designers, traffic engineers, and other practitioners: Human Factors Guidelines for Road Systems (HFG). The HFG is intended to: (1) serve as a resource document for highway designers, traffic engineers, and other practitioners, (2) provide the best factual information and insight on road users’ characteristics, and (3) facilitate safe roadway design and operational decisions.

Published in 2012, NCHRP Report 600 is the first complete holistic release of the Human Factors Guidelines for Road Systems (HFG) Second Edition (HFG2). The HFG2 provides data and insights from the scientific literature on the needs, capabilities, and limitations of road users, including: perception and effects of visual demands, cognition and its influence of expectancies on driving behavior, and individual differences such as age and other factors. The HFG2 assists practitioners in safety, operations, and design in developing a greater understanding of road users’ capabilities and limitations and how these issues could be incorporated into day-to-day decision making. The HFG2 has 21 guideline chapters and 90 guidelines. NCHRP Project 17-80 (HFG3) updated two of the chapters (Chapter 5: Sight Distance, and Chapter 10: Unsignalized Intersections) and added three new chapters (Pedestrians, Bicyclists, and Roundabouts).

The objectives of this current project (NCHRP 22-46) are to: (1) prepare a Human Factors Guidelines for Road Systems, Fourth Edition (HFG4), which can be used by State Department of Transportations (DOTs) and other transportation agencies to integrate Human Factors (HF) principles into design and operations across roadway systems for all road users, (2) provide a supplement to the AASHTO HSM with other safety tools and processes such as RSAs, operational reviews, performance planning, and crash data analysis for road system design and operations, and (3) document (very broadly) 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. For this research, road users include, but are not limited to, drivers, pedestrians, bicyclists, motorcyclists, and electric scooter users.

This final report summarizes the activities and results associated with the 22-46 project. The body of this report contains three technical sections:

• Section 1 provides an introduction to this report and the overall project.
• Section 2 summarizes the objectives, methods, and results of Tasks 1 through 6 (Assess Existing Human Factors Literature, Develop Draft Practitioner Survey, Conduct Practitioner Survey, Develop Recommendations to Update the Content of the HFG, respectively, Develop Workplan and Interim Report, and Develop Updated Content for the HFG4).
• Section 3 summarizes the Project Team’s recommendations for future research needs and priorities.