Comprehensive Human Factors Guidelines for Road Systems (Web-Only Document) (2005)

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APPENDIX B HUMAN FACTORS GUIDELINES FOR ROAD SYSTEMS DRAFT INTRODUCTORY CHAPTER CHAPTER 1 WHY HAVE HUMAN FACTORS GUIDELINES FOR ROAD SYSTEMS? B-1

TABLE OF CONTENTS 1.1 Overview of Human Factors Guidelines for Road Systems: Design and Operational Considerations for the Road User.............................................................. B-3 1.2 What is “Human Factors?”................................................................................ B-3 1.2.1 The Discipline of Human Factors and Its Relation to Traffic Engineering.... B-3 1.2.2 Hallmarks of the Human Factors Approach ................................................... B-5 1.3 Why are Human Factors Guidelines for Road Systems Necessary? .................. B-6 1.3.1 Limitations of humans factors incorporated into standards and guidelines.... B-6 1.3.2 Meeting road user system needs ..................................................................... B-7 1.3.3 Understanding and addressing when human factors problems occur............. B-8 1.4 Purposes That This Document Serves................................................................. B-8 1.4.1 Uses of This Document................................................................................... B-8 1.4.2 What This Document is Not ........................................................................... B-9 1.5 References ........................................................................................................... B-9 B-2

1.1 Overview of Human Factors Guidelines for Road Systems: Design and Operational Considerations for the Road User Human Factors Guidelines for Road Systems: Design and Operational Considerations for the Road User is a guidance document that brings human factors principles and findings to the highway designer and traffic engineer. It will allow the non-expert in human factors to more effectively bring consideration of the roadway user into practice about design, operations, and safety. The Human Factors Guidelines serves as a complement to other primary design references and standards. It does not duplicate or replace them. It is an additional tool for the engineer to use in designing and operating roadways that are safe and efficient – roadways that are safely usable by the broad range of roadway users. The document is divided into four parts. “Part I: Introduction to the Human Factors Guidelines,” is a short introduction to the document. This first chapter explains why it is useful to have such guidance. The second chapter explains how to use the document and take advantage of its features. “Part II: Bringing Road User Capabilities Into Highway Design and Traffic Engineering Practice” describes a human factors approach to roadway design, presents basic principles and methods, and provides key information about basic road user capabilities. Part II is about road users and how to take their needs into account. It is the basis from which the guidance in Parts III and IV is derived. Parts III and IV present the actual guidance statements within this document. “Part III: Human Factors Guidance for Roadway Location Elements” is organized around specific roadway location elements, such as signalized intersections and work zones. “Part IV: Human Factors Guidance for Traffic Engineering Elements” deals with traffic engineering elements such as fixed signage, variable message signs, markings, and lighting. The guidance among many of these chapters is interrelated and the chapter sections link to one another. Chapter 2 (in Part I) explains how the guidance chapters are organized and how they can be searched and used. 1.2 What is “Human Factors?” 1.2.1 The Discipline of Human Factors and Its Relation to Traffic Engineering Application of good human factors principles, in useful guideline form for the practitioners who design and operate streets and highways, is fundamental to the safety of all road users. The ITE Traffic Engineering Handbook (Pline, 1999) cites a definition of “traffic engineering” as “that branch of engineering which applies technology, science, and human factors to the planning, design, operations and management of roads, streets, bikeways, highways, their networks, terminals, and abutting lands.” Thus the discipline of human factors is recognized as an integral contributor traffic engineering practice. However, many highway designers and traffic engineers do not have a clear understanding of what human factors is and how its principles are relevant to their work. B-3

Human factors is the scientific discipline that studies how people interact with devices, products, and systems. It is an applied field where behavioral science, engineering, and other disciplines come together to develop the principles that help assure that devices and systems are usable by the people who are meant to use them. The field approaches design with the “user” as its focal point. Human factors practitioners bring expert knowledge concerning the characteristics of human beings that are important for the design of devices and systems of many kinds. The discipline contributes to endeavors as complex as space exploration and to products as simple as a toothbrush. In the field of transportation engineering, there have been numerous important contributions from human factors, but these are not always self-evident. Sight distance requirements, workzone layouts, sign placement and spacing criteria, dimensions for road markings, color specifications, sign letter fonts and icons, signal timing – these and many more standards and practices have been shaped by human factors evaluation. As applied to highway safety, human factors is concerned with the design of the roadway and operating environment and the vehicle. The three primary components of the highway transportation system – the roadway, the vehicle, and the road user – all must be compatible with one another. Engineers can design roadways, traffic control devices, and vehicles, but they cannot design the road user. They can design for the road user. Human factors provides an objective basis for doing this. It is based on measured behavior and capabilities rather than assumptions or trial-and-error. Of course, roadways have been designed for many years while the science of human factors was still maturing as a discipline that could provide reliable contributions. The needs and abilities of road users were not ignored, but they were not fully and systematically included either. Fortunately, the human being is very adaptable. That is why over history, complex man-made systems have been able to evolve and work reasonably well, even though inadequate consideration was given to the needs of the human user. The transportation system in general, and the highway system in particular, certainly provide good examples of this. One cannot deny the success of modern traffic engineering practice. In the U.S. in 2001, nearly 200 million drivers of extremely varying capabilities shared the roadways while logging almost three trillion travel miles in relative safety and efficiency (NHTSA, 2002). In many cases, this is because the road user is able to adapt to the demands of the driving environment, not because the driving environment has been adapted to the user. At the same time as we acknowledge the successes of the system, we must also recognize its limitations. In 2001, there were over six million police-reported (and many more non-reported) collisions in the U.S., with attendant loss of life, property, and productivity (NHTSA, 2002). Some form of operator error is often a contributing factor in highway crashes. “Error” means the road user did not perform his or her task optimally. Misperceptions, slow reactions, and poor decisions are the products of a poor match between the needs and capabilities of drivers and the task demands that they face on the roadway. A more driver-centered approach to highway design and operation will promote continued improvements in highway safety. There has been greater and greater awareness and acceptance of this insight over recent years. B-4

Traffic engineering practice certainly did not develop ignoring the driver. But systematic data on driver capabilities and performance as a resource for design practice is relatively recent. The body of what we now label “human factors” research began in the 1950s (primarily in the area of highway sign design) but really began to advance meaningfully only in the 1960s, long after many standards and practices were established. Roadway user human factors research accelerated over the next decades. This ever-growing body of knowledge has gradually made inroads into design and practice. However, a user- centered perspective is still not characteristic for many practitioners. In part, this is because the now large body of knowledge regarding the roadway user is not easily usable. It is not organized, summarized, explained, and made accessible to the engineer. It is not tied in a useful way to the everyday tools and resources used by the engineer. 1.2.2 Hallmarks of the Human Factors Approach There are some important fundamental principles that characterize the human factors approach to designing things. These characteristics are compatible with the goals of highway designers and traffic engineers and help explain why human factors practice so successfully complements traditional traffic engineering approaches. Part II of this document explains these distinguishing qualities and how they contribute to highway design and operational practice. Briefly, some of the most important hallmarks of the human factors approach are these: • User-centered design. The human factors approach to design begins with understanding the task to be accomplished, from the user’s point of view. A “task” may be something like avoiding an obstacle, selecting an appropriate path for the vehicle, or deciding whether to accept a gap to make a maneuver. The analysis then examines what information the user needs to accomplish the task and considers this along with the capabilities, knowledge, and motivations of the range of potential users. When the design of a device or system is consistent with the characteristics and needs of the user, performance is more rapid and reliable and less prone to error. • Empirically-based science. Human factors is based on a scientific approach with empirical measurement at its core. It is not a “soft” discipline of a speculative nature. Wherever possible, it is based on empirical measurement of human capabilities and behavior in relation to engineering design, collected under rigorously controlled conditions, including laboratory, driving simulator, traffic observational, and instrumented vehicle studies. Human factors brings to traffic engineering both an empirical base of fundamental human capabilities and specific data on driver behavior under various conditions. • Systems perspective. A highway designer or traffic engineer may deal with one element at a time, for example the design or delineation of a roadway curve. But to the roadway user, everything occurs in a broader context, and this can matter very much. Features and events on the road seldom appear as isolated events. The road user is dealing with multiple concerns at any moment and is influenced by preceding events, anticipated events, multiple sources of information, and competing demands. The human factors scientist seeks to understand how people B-5

are likely to behave when they encounter the designed element in its real-world context. • Focus on behavior. The design and traffic engineers are concerned with the performance of the highway system – operational efficiency and safety. Human factors specialists are concerned with the behavior of road users, which is among the important determinants of highway system performance. Human behavior is rarely simple and people can vary greatly from one another. Therefore the human factors field must deal with the range and complexity of road user capabilities and behaviors in relation to engineering design. • Life-cycle application. Human factors can and should contribute to the design and operation of a device or system throughout the product life cycle. This means that human factors concerns enter into initial planning, design, construction, operation, evaluation, and maintenance. The earlier in the process human factors considerations are dealt with, the more beneficial it may be. This brief overview should help clarify what “human factors” means and how it contributes to the goals of the roadway designer and traffic engineer. Part II of this document provides a much richer discussion and more examples. 1.3 Why are Human Factors Guidelines for Road Systems Necessary? Why is it necessary to have a document on “human factors guidelines for road systems?” Even granting the importance of roadway user characteristics, isn’t this already incorporated into the basic standards and guidelines for highway design and traffic engineering? It might seem that the human factors considerations ought to be transparent to practitioners. The human factors components that contribute to design equations and operational parameters do not have to be understood in order to follow standard practice. However, there are some important reasons why the highway designer or traffic engineer needs to be aware of key human factors concerns. It is not necessary for them to become human factors experts, but it is important to be able to think in human factors terms and have access to human factors data and methods. Some reasons why guidance on human factors is required for road system design and operations are listed below. 1.3.1 Limitations of humans factors incorporated into standards and guidelines Some practitioners have the misperception that human factors are fully and adequately considered and integrated into current standards and guidelines. Although some practices are based on extensive, well-documented, and fully appropriate behavioral data, this is certainly not always the case. Existing standards and guidance include the following limitations: • Many practices do not have any empirical basis. They were not developed based on data to begin with and have not been formally evaluated for adequacy for road users. • Some practices are based on outdated or inadequate behavioral data. While some practice may have been justified based on limited observations made forty years ago, the measured behavior may no longer be representative of current behavior, B-6

given changes over the years in roadways, vehicles, traffic, operations, and even drivers. • Both the roadway system and human behavior are complex and there may be some applications where a minimum design requirement is insufficient to support the desired driver behavior. • Some practices are based on simple models of what road users see or do. These models may work well for most cases but may over-simplify other situations. • Design equations are based on certain operational and user behavior assumptions and these assumptions are not always met. • Technology and operations are constantly evolving. Design decisions have to be appropriate to current and emerging environments and options. Standards and guidelines may not keep pace with changes in communications technology, vehicle features, roadway features, roadside environment, traffic control devices, or traffic operational characteristics. • There may be particular human factors concerns for special user groups and these concerns may have prominence for certain applications. With the aging of the general population, there has become much greater concern with older road users, although their needs are not fully reflected in standards and practice. Examples of other road user groups of emerging importance include visually impaired pedestrians, pedestrians with mobility limitations, heavy truck operators, and users of lower-speed alternative transportation devices. • Under real-world conditions, there may be cases where it is not possible to meet certain specifications or where there is a requirement for a trade-off between two or more conflicting demands. The impacts on user behavior must be carefully considered. • There may not be standards or guidance to deal with particular combinations of features that may impact human performance. For these reasons, it is unwarranted simply to assume that current practice already takes adequate consideration of human factors concerns for all situations. With appreciation and guidance on human factors issues, the practitioner can better recognize where additional user-centered design concerns arise. 1.3.2 Meeting road user system needs Those who design and operate the roads need to be able to see the situation from the perspective of the roadway users who must use their products. Road users are not narrowly focused on some particular roadway element or design feature. Rather, they are influenced by all of the factors present at a site, as well as broader features of the roadway network and by features and events leading up to the site. Unfortunately, it is often difficult for a practitioner to acquire this “big picture.” The highway design and traffic engineering community is becoming increasingly specialized, with different trades or specialties (lighting, traffic control devices, signing, landscaping, etc.) providing specific contributions at various phases of the design and development process. These interests may be brought in at various stages of design to manage different aspects. This diffusion of responsibilities makes it difficult for the various contributors to fully appreciate the needs of road users as they confront the situation in its full context. A B-7

document that provides human factors principles and guidelines will help highway designers and traffic engineers to evaluate their efforts in a more appropriate and more complete context. 1.3.3 Understanding and addressing when human factors problems occur If a safety or operational problem arises, is it due to a human factors problem? Is there a human factors approach to rectifying the problem? The Human Factors Guidelines for Road Systems can help answer these questions. The extensive use of linking among sections and chapters of this document (see Chapter 2) allows the engineer to find the guidance, principles, and data that will help clarify and address the human factors issues. The guidance can also serve as a complement to other sources of diagnostic tools and techniques, such as safety audits or the Highway Safety Manual (Hughes, Eccles, Harwood, Potts, and Hauer, 2004). In summary, there are important reasons why highway designers and traffic engineers need access to human factors guidance. It is not warranted to simply assume good human factors is incorporated into every design practice for every situation or that current guidance adequately covers all applications. The user-centered approach of human factors emphasizes that devices and systems are always designed for someone, and the system is improved when the design and traffic engineer understand and encompass the needs and abilities of the range of users. 1.4 Purposes That This Document Serves The Human Factors Guidelines for Road Systems is intended to serve a number of important purposes. There are also some things this document is not meant to be and the reader should not expect. 1.4.1 Uses of This Document • The Human Factors Guidelines for Road Systems provides an introduction to the field of human factors as it is applied to highway design and traffic engineering. It presents the basic concepts and methods and provides fundamentals of road user behavior. It summarizes key data on basic road user capabilities, such as visual acuity, response time, and the distribution of visual attention. • The Human Factors Guidelines for Road Systems provides guidance for more optimal design of highways and traffic control devices. This guidance helps indicate when, where, and how user-based considerations may offer design criteria that may be more effective than minimal design values or typical practice. • The Human Factors Guidelines for Road Systems links human factors data and analysis with related guidance in other key highway design and traffic engineering reference documents. This will help the user in critically assessing the suitability of recommendations, minimum specifications, or options in other documents. • The Human Factors Guidelines for Road Systems provides help in problem solving. When faced with a problem that may be related to road user B-8

considerations, the guidance can help identify probable human factors causes or countermeasures. The document is constructed so that links among chapters and sections help the reader connect related issues, provide key background information when needed, and relate site features and traffic engineering elements. • The Human Factors Guidelines for Road Systems provides an objective resource for support and justification in decision making. The guidance, rationale, background, and principles provide a defensible basis for deviating from normal practice when that normal practice is not optimal from a road-user-based, highway safety standpoint. 1.4.2 What This Document is Not • The Human Factors Guidelines for Road Systems is not an alternative to primary design references in highway design and traffic engineering. It is intended to complement and amplify aspects of these other references, such as the Manual on Uniform Traffic Control Devices, the AASHTO A Policy on Geometric Design of Highways and Streets, the Traffic Control Devices Handbook, the Highway Safety Manual, and other guidance. As a supplement, it is not intended to provide comprehensive design specifications or be redundant with the treatment of other documents. The Human Factors Guidelines for Road Systems is meant to add to, and refine, existing guidance. • The Human Factors Guidelines for Road Systems is not a textbook or tutorial on human factors or a comprehensive source of human factors literature. It is primarily a source of guidance with technical backup and explanation. It does serve an educational purpose, in that Part II (Bringing Road User Capabilities Into Highway Design and Traffic Engineering Practice) in particular informs the non- expert about human factors perspectives, methods, theory, and data. However, many users of the document may make use of the guidance without ever fully reading Part II. There already exist a number of detailed books and courses on the role of human factors in highway design and safety. The educational function of the Human Factors Guidelines is a limited one and it is not intended to create experts in the field of human factors. • The Human Factors Guidelines for Road Systems is not a guide to crash investigation or a comprehensive reference for safety diagnosis. Its content may certainly aid in interpreting crashes and safety/operational problems, but it is not a manual for that purpose and it is specifically focused on human factors, not the fully array of potentially contributing causes. However, various chapters of this document do contain recommended diagnostic approaches for dealing with specific human factors problems. 1.5 References Hughes, W., Eccles, K., Harwood, D., Potts, I., and Hauer, E. (2004). Development of a Highway Safety Manual. NCHRP Web Document 62: Project 17-18(4): Contractor’s Final Report. Transportation Research Board, Washington, DC. B-9

NHTSA (2002). Traffic Safety Facts 2001: A Compilation of Motor Vehicle Crash Data from the Fatality Analysis Reporting System and the General Estimates System. National Highway Traffic Safety Administration, Washington, DC. Pline, J. (Editor) (1999). Traffic Engineering Handbook. Institute of Transportation Engineers, Washington, DC. B-10