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

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6.0 Example Chapters Two chapters were written as an initial basis for the HFG. One of these was the first, introductory chapter. This is a short introduction to the purpose of the document and its general content and use. The introduction does not contain any detailed technical material or guidance. The other chapter is a sample chapter from the portion of the HFG that provides guidance. The particular chapter selected – “From Driver Reaction Time, Maneuver Time, and Speed to Design Distances: General Guidelines” – was selected as the example chapter after extensive outside consultation and discussion. It is intended to serve as a “straw man” model for subsequent chapters and also to serve as a stand-alone document for its potential interest and use now for its particular topic area. The example chapter is referred to a “Chapter 5” for consistency with the proposed HFG outline (see Section 4.0). It is recognized that the chapter number may likely change in the course of the development of the HFG, but a chapter number was designated to help clarify the status of this chapter as an integrated element of a larger, interactive document. Section 6.1 describes the considerations that went into the selection of the sample chapter. Section 6.2 provides introductory discussion for Chapter 1, “Why Have Human Factors Guidelines for Road Systems?” Section 6.3 provides introductory discussion for Chapter 5, “From Driver Reaction Time, Maneuver Time, and Speed to Design Distances: General Guidelines.” The full chapters themselves are attached to this report as appendices. Chapter 1 may be found in Appendix B and Chapter 5 in Appendix C. The HFG is envisioned to be a CD-ROM based document that is highly interactive. Users will be able to move from section to section via linking options and material will be shared between sections. The HFG will also be able to employ dynamic displays made possible by the medium. Therefore we may expect animations, video, and interactive elements. Since the example chapters provided here (Appendix B and C) do not share these capabilities, they are simulated in the sample chapters. Links are shown in brackets, using boldface [Section X.X]. This is intended to show where a link would allow the reader to obtain more information by jumping to another chapter, or another document altogether if Web-accessible. A few examples of potential animation are included as well. In these cases, text is inserted describing the animation and how it would be used. 6.1 Selection of the Sample Chapter The sample chapter was intended to serve two purposes. One purpose was to provide a “straw man” example for review as model HFG chapter. This chapter is expected to be subjected to broad external review and critiqued for format, content, style, appropriate depth of treatment, additional features, and so forth. It is a step in the process of evolving the HFG. The ultimate version of this chapter might look quite different. The second purpose was to provide a useful, stand-alone product on the topic of the sample chapter. Quite aside from its role as a model for the HFG, the effort in producing this chapter should produce a technical work that is of current use to the field. 29

Both of these considerations were given weight in the process of selecting the sample chapter. However, the two goals were not entirely compatible. Since the HFG is viewed as an electronic document consisting of a highly integrated collection of interrelated chapters, with extensive cross-linking, a “stand alone” chapter is not fully consistent with that vision. Furthermore, some topics may function well as typical model chapters but not serve well as independent documents. Other topics may function well on their own but not be very typical of most HFG guidance chapters. Some topics may be of particularly strong interest for application, but are very complex and thus are not good first models; others may be relatively straight-forward, but of more limited appeal. An extensive process of outside review and opinion was provided to the project team for purposes of sample chapter selection. The intent was to have the sample chapter selection reflect the interests and opinions of the various outside parties interested in the development of the document, in addition to those of the NCHRP project panel and the project team. The issue was presented to the NCHRP project panel, the TRB Joint Subcommittee for Development of International Human Factors Guidelines for Road Systems, TRB technical committees with related interests, and others concerned with the HFG. The issue was discussed as an agenda item at open meetings of the Joint Subcommittee during the TRB Annual Meetings, preliminarily in January 2003 and further in January 2004. In addition, a presentation was made at the October 2003 Annual Meeting of the Human Factors and Ergonomics Society. There was a wide variety of opinion on the sample chapter with little initial agreement. Some favored a basic chapter on fundamental human factors principles or data (a Part II chapter) as a useful stand-alone product and logical first step; however, this would have minimal relevance as a model for typical guidance chapters (Parts III and IV). Some favored the choice of a relatively simple and conscribed (in human factors terms) guidance chapter, such as one on rail-highway grade crossings. This was seen as having manageable scope, well-delineated human factors issues, and less dependency on cross- referencing than some other chapters might require. Others favored selecting a chapter on particularly significant safety problems, such as intersections. This would be a complex chapter to develop as a first step, and might interrelate to other chapters in a substantial way. Finally, some recommended the chapter on sight distance (time and speed). It has the virtue of dealing with key concepts that will relate to subsequent chapters, yet (unlike sections in Part II) provides specific guideline statements. However, these guidelines are likely to be at a more general level than for other chapters that are more specific to a roadway location element (e.g., curve, intersection) or traffic engineering element (e.g., signing). The sight distance chapter is in some ways a bridge between Part II and Part III of the HFG. After considerable discussion, a general recommendation emerged from the panel and Joint Subcommittee that the sight distance chapter be selected. While there was not complete consensus, this appeared to be the most agreeable choice and was also reasonable to the project team. Although it is not entirely typical as a guidance chapter, it does serve as an example of guidance and at the same time provides a topic that can be the basis of a useful stand-alone document. Therefore Chapter 5, “From Driver Reaction 30

Time, Maneuver Time, and Speed to Design Distances: General Guidelines,” is the chapter that was developed. This represents an important human factors topic for traffic engineering and roadway design and is at a general enough level to serve as a useful stand-alone document. However, it should be kept in mind that this chapter is not likely to be typical of subsequent chapters in terms of the specificity of the applications. 6.2 Introductory Chapter (Chapter 1. Why Have Human Factors Guidelines for Road Systems?) Chapter 1 explains the need for human factors guidelines and the purposes for which the document is intended. It is an intentionally brief chapter that is meant to convey that there is something useful for the designer/engineer here. This introductory chapter does not contain guidance or technical detail. Part II of the HFG will contain the more extended discussion of human factors concepts, data, and principles, while Parts III and IV will provide the explicit guidelines. This chapter is envisioned as one of two chapters that comprise Part I of the HFG. It is comprised of three general sections: • What is Human Factors? • Why are Human Factors Guidelines for Road Systems Necessary? • Purposes of This Document The other complementary chapter in Part I will be “Chapter 2: How to Use This Document.” It will deal more with the mechanics of how to use the document and the guidelines. Chapter 2 will need to be written as the HFG develops and expands beyond a single sample chapter and has actual search and linking capabilities. It will describe the content and organization of the document, the format of the background and guidance sections, search capabilities, relationship to and use with other standards/guidelines, and reference documents, and links to related resources. Chapter 1, then, succinctly defines the field, scope, need for, and function of the document. Because the primary (though not sole) purpose of the HFG is provide guidance for practicing traffic engineers and highway designers, the introductory chapter must address possible lack of knowledge and misconceptions from readers who are not well-versed in human factors. While Part II of the HFG provides more full explanation regarding the field, Chapter 1 must overcome these barriers to appreciation of the relevance of the document. Among the concerns that must be explicitly addressed are: • The scientific nature of the discipline of human factors and how it directly relates to traffic engineering/road design issues • What human factors brings that is unique and complementary to existing practice • The misperception that driver behavior and human factors considerations are already fully and adequately incorporated into design standards • The difference in the perspectives of ordinary road users and those of road designers/traffic engineers and why this matters The introduction must also portray the HFG as a useful and usable supplement to the resources that designers and engineers already use. It must be shown to be an aid and not another burden. While all of these issues require some depth of discussion, those more technical expansions are appropriate for Part II of the HFG. Chapter 1 provides the 31

opportunity to explain succinctly the purpose of the HFG and the reasons why it may be helpful to the practitioner. 6.3 Sample Guidance Chapter (Chapter 5: From Driver Reaction Time, Maneuver Time, and Speed to Design Distances: General Guidelines) Section 6.1 already discussed the process of the selection of the sample chapter and some of its considerations. The sample chapter is titled “From Driver Reaction Time, Maneuver Time, and Speed to Design Distances: General Guidelines” and is referred to as Chapter 5 of the HFG. This chapter deals with sight distances and how they are related to the human behavioral and perceptual aspects of perception-reaction time, maneuver time, and speed. Sight distance is a fundamental design concept, but it is not a behavioral one. The human factors is in the behavioral components that generate the design distance requirements. Hence the title of this chapter, which considers the human factors of the component driver processes and how they lead to distance needs. The chapter is referred to as “Chapter 5” based on the HFG outline in the November 2002 Task 2 Report for this project. It is recognized that chapter numbers may be different from those in the outline as the document evolves. This chapter is seen as the first “guidelines” chapter in the HFG. It is somewhat unique from subsequent guidance chapters in that it is not specific to a roadway location element (e.g., curves) or traffic engineering element (e.g., signing). The guidance principles are therefore at a somewhat more general level than in subsequent chapters. Design distance issues that are specific to a particular roadway location element or traffic engineering element will be treated in detail in the appropriate chapters. Differences among applications are dealt with here, but within this chapter the emphasis is on principles that are relevant to many design conditions. In this sense, Chapter 5 is something of a bridge chapter between Part II of the HFG, which provides basic human factors concepts, findings, and approaches, and Parts III and IV, which provide specific guidance statements for particular applications. The chapter is comprised of five sections and an appendix. Section 5.1 is a background section that describes the human factors issues and chapter objectives, and indicates how the chapter is related to other key reference documents. Section 5.2 provides the technical treatment and guidance for design sight distance, broken into subheadings that reflect the major sight distance design criteria: stopping sight distance, intersection sight distance, decision sight distance, and passing sight distance. Section 5.3 addresses the influence of design on speed; since speed (V term) is a key element of sight distance design equations, the human factors concerns of speed determinants directly impact sight distance needs. Section 5.4 provides an approach to diagnosing human factors-related sight distance problems. Section 5.5 is the chapter reference citation section. The attachment (Appendix A of the sample chapter) provides an example application of the Section 5.4 diagnostic procedure. This chapter structure is somewhat different from the original chapter outline (submitted under Task 6 of this project). The original vision of the chapter outline proposed major 32

headings for Perception-Reaction Time (5.2) and Maneuver Time (5.3), and within each of these, subsections for the various types of sight distance. In practice, this turned out to be unwieldy, repetitive, and hard to use. It was more useful to have perception-reaction time, maneuver time, and sight distance as subsections under each sight distance type, rather than sight distance types as subsections under other separate headings. In this way, all of the considerations for a given design application (e.g., stopping sight distance) are in one place. Because Chapter 5 is intended to serve as a stand-alone document on human factors and sight distance, beyond its “straw man” model chapter role, the introductory section of the chapter is somewhat unusual. This introduction precedes Section 5.1, which is the actual beginning of the chapter itself. The introduction contains background information (parallel to information contained in this report) that explains the purpose and features of the chapter. It explains how this sample chapter may differ somewhat from more typical Part III and IV chapters of the HFG. Such an introduction obviously will not be typical of actual HFG chapters, but is necessary in Appendix C if the chapter is to function in a stand-alone mode. Also, the chapter contains more extensive introductory discussion than would be anticipated in most chapters, since there are no existing supporting chapters to which links may be made. 33