Comprehensive Human Factors Guidelines for Road Systems (Research Results Digest) (2005)

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Research Results Digest 296 April 2005 SUMMARY This digest summarizes the final report for NCHRP Project 17-18(8) (available as NCHRP Web Document 70). This is the initial project to develop a new resource document for highway designers, traffic engineers, and other practitioners. The Human Factors Guidelines (HFG) will provide the best factual information and in- sight on road users’ characteristics to facil- itate safe roadway design and operational decisions. Project 17-18(8) developed an outline for the first edition of the HFG, a work plan, and Chapters 1 and 5, “Intro- duction” and “From Driver Reaction Time, Maneuver Time, and Speed to Design Dis- tances: General Guidelines,” respectively. An interim edition of the HFG will be available in late 2007. INTRODUCTION The effort to significantly reduce high- way fatalities and injuries is a huge under- taking, especially in the United States and Europe, which each experience more than 40,000 highway fatalities each year. Effec- tive and acceptable solutions to this prob- lem require that consideration be given to the three key components of highway transportation: road, vehicle, and road user. Often forgotten are the needs and constraints of the road user. The impetus behind this project was the recognition that current design references have limitations in providing the practitioner with adequate guidance for incorporating road user needs and capabilities when dealing with design and operational issues. These limitations may be of various sorts. Design guidelines may represent minimum requirements that are not always appropriate over the full range of roadway users or applications. Guidance may not be based on adequate human factors data. Guidance documents may not offer sufficient explanation so that practitioners can make effective use of be- havioral factors. Conflicting requirements or unusual conditions may make it difficult to comply with ideal design parameters and require some basis for a compromise. Design practice may be driven by concerns about cost and compliance, without a basis for also incorporating safety benefits through user-centered design. Because of such limitations to current design guides, it would be beneficial to provide guidelines to assist the practitioner in identifying and COMPREHENSIVE HUMAN FACTORS GUIDELINES FOR ROAD SYSTEMS This digest presents the results of NCHRP Project 17-18(8), “Comprehensive Human Factors Guidelines for Road Systems.” This project developed an outline, two chapters, and a work plan for the first edition of the Human Factors Guidelines. This digest is based on a draft final report authored by the principal investigator, Neil Lerner, Westat, Inc.; Robert Llaneras, Westat, Inc.; Alison Smiley, Human Factors North; and Fred Hanscom, Transportation Research Corporation. Subject Area: IVB Safety and Human Performance Responsible Senior Program Officer: Charles W. Niessner NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM

addressing human-centered safety concerns in road- way design and operations. The HFG is seen as a complement to other primary design guides, such as the 2001 AASHTO Geometric Design Guide and the FHWA’s 2003 Manual on Uniform Traffic Control Devices (MUTCD). The HFG is seen as a collaborative, evolving document that is expected to be the product of many contributing authors over a period of years. The document may continue to expand and be re- fined over subsequent versions. The development and growth of TRB’s 2000 Highway Capacity Manual provides a successful model for this type of approach. RESEARCH OBJECTIVE The objective of NCHRP Project 17-18(8) was to lay the groundwork for a first edition of the HFG. The project developed recommendations for the content, format, organization, and capabilities of the HFG. It developed an outline of the document and a detailed work plan for the effort required to produce a first edition. As part of this effort, a draft introduc- tion and one sample chapter were written. GENERAL RECOMMENDATIONS FOR DESIGNING THE HFG Target Users of the HFG The general purpose of the HFG, as defined in the project Statement-of-Work, is to provide the “best factual information and insight” regarding road user characteristics so as to “facilitate safe roadway design and operational decisions.” There- fore, although there may be many groups who may make use of the document, the primary audience is practitioners dealing with design and operational is- sues in their normal course of work. This audience is not assumed to have expertise in human factors. There may be little understanding of what the field is and little motivation to seek in- sights, data, or guidance in this area. While the need to incorporate road user capabilities into design and operational decision making has certainly become more widely appreciated in recent years, apprecia- tion and knowledge are by no means universal. Therefore, if the HFG is to be used as an everyday resource, it must appeal to and be understood by the range of practitioners, including those with little background in human factors issues. It should also be noted that not all those providing traffic engi- neering functions are trained engineers. The HFG should be written in a straightforward and nonaca- demic manner, but must remain appropriate for trained professionals. It should be at the level of an introductory textbook. There is an important distinction to be made be- tween the role of the highway designer and that of the traffic engineer. They address road user require- ments at different points in the process and use their own distinct tools in addressing driver needs. Both groups need to be cognizant of user-centered con- cerns in the design and operation of roadways. De- signers and traffic engineers are likely to approach the HFG in different ways and for different reasons. Both groups must be recognized as distinct parts of the audience for the document. Functions and Objectives of the HFG There are various functions that a document called Human Factors Guidelines might serve. Questions about exactly what the HFG will attempt to accomplish were quite in evidence at the work- shop conducted by the TRB Joint Subcommittee for Development of International Human Factors Guidelines for Road Systems, A3B02(2). There were questions such as, Is this material “tutorial or referential in nature?” The emphasis placed on var- ious functions will guide the shape of the document. The general functions that the HFG might serve in- clude the following: • Identify the probable causes and countermea- sures when faced with a problem related to road user characteristics. • Provide proactive guidance to include human- centered concerns in design and planning and to avoid potential user-related problems. • Promote the understanding of an appropriate road user–centered perspective of safe design. • Educate about fundamental human factors principles related to highway safety. • Provide a defensible basis for deviating from normal practice when that normal practice is not optimal from a road user–based, highway safety standpoint. • Provide adequate documentation as a resource for defense of a design or operational decision. • Provide an independent and authoritative basis to reject politically pressured, inappro- priate design or operational suggestions. 2

All of these functions are interrelated, and all must be addressed to some degree by the HFG. The first two functions (probable causes and proactive de- sign guidance) are the day-to-day uses of the HFG and should be the primary drivers of the document’s structure. While the HFG will serve an important ed- ucational function, it should not be viewed as a text- book or a source of technical literature. There already exist a variety of substantial books on human factors for highway safety and traffic engineering. The HFG is not intended to be a repository for all relevant human factors concepts and differs from these more didactic references. Its focus is on guidance, and the guidelines are organized around traffic engineer- ing/highway design concepts, rather than around human factors concepts. The HFG must include ed- ucational material on human factors concepts, but it must be streamlined and the guidelines themselves must be structured around engineering factors. The HFG should be viewed as a complement to major design references. It should not duplicate or re- place them. This means that the HFG does not have to explicitly address every design aspect treated in other sources. For example, it may not be appropri- ate to specify the placement of a particular traffic control device (e.g., arrow board) for a work zone if this is specified elsewhere. However, the HFG does need to deal with the limitations of existing guidance, define conditions where other factors come into play, and help the practitioner in recognizing the need for trade-offs and making decisions. While guidance should include quantitative information wherever possible, the guideline should not be prescriptive. In many cases, the need for additional human factors consideration comes from the fact that there is an un- usual situation or conflict among guidelines so that a “cookbook” approach is not appropriate. The guide- lines need to provide the principles and data to allow the engineer to work through the problem. The HFG should serve as a supplement to primary design guides, and as such the specific guidance needs to be problem based or treated on a by-exception basis, rather than attempting to specify and justify every as- pect of roadway design and operations. The HFG must be more of a tool than a cookbook. Because the HFG may often serve a problem- solving need rather than an educational one, it should not be assumed that users will enter the doc- ument at the beginning and read the introductory and background chapters. Users will typically enter searching for specific guidance on a particular issue. Therefore, it will be important to provide cross- referencing to sections that deal with fundamental human factors principles that may relate to some specific guideline. The early sections of the HFG should be written in an inviting manner and at a level of detail that does not deter prospective readers. Nonetheless, no guideline statement should presume that background chapters have been read. Media and Capabilities The project Statement-of-Work specified that the HFG would be developed in a CD-ROM format. While a variety of alternative media were reviewed as part of this project, CD-ROM has been the focus and offers a variety of virtues as a format for the HFG. Although some users may simply want to print hard-copy versions of the handbook (or rele- vant sections), others may want to access more ad- vanced features of the HFG (search the handbook, gather in-depth reference materials, view graphic il- lustrations or simulations of guideline concepts, or link to other resources). The tool must support these levels of interaction while retaining high-end fea- tures and capabilities that can be accessed by others desiring the full range and functionality of multime- dia. A multimedia program can provide a nonlinear environment with a united structure that is easy to use and that provides depth of content for the user. The CD-ROM is a convenient format for deliver- ing high-quality visual and interactive multimedia content. As a result of the large file sizes that can be used on a CD-ROM, the content can be far more media oriented, providing video clips, detailed three- dimensional animations, and a host of other tech- nologies. CD-ROM can also be linked to the Internet, providing additional advantages of fast delivery from a CD-ROM and ability to update from the Internet. This combination is ideal for accessing related infor- mation and handbooks. Content on a CD-ROM can also be designed and structured so that it can be con- verted to web-based delivery. The low replication costs of CD-ROMs and the wide availability of com- puters with CD-ROM drives make this an extremely practical format. While the information stored on CD- ROMs cannot be updated, links to other documents and the Internet can be provided; this flexibility en- ables time-sensitive information to be readily up- dated. The flexibility afforded by a CD-ROM and the multimedia capabilities that it brings makes this an ideal tool for this type of application. A CD- ROM–based human factors handbook has the poten- tial to provide traffic engineers with an informative and interactive tool that will help them to apply 3

known research and guidelines to solve design issues, as well as provide opportunities for them to access ex- tensive reference materials and link to other fre- quently used resources (manuals, handbooks, etc.). The ability to search the HFG document is viewed as a crucial and beneficial feature that can help users access desired and relevant information quickly and easily. This capability is greatly facili- tated by electronic search engines and is expected to be a significant advantage of the CD-ROM over hard copy. Unfortunately, there is no standardized set of features or user interfaces common to most search engines. Some can possess complex or difficult-to- use interfaces and lack important search features, leading to confusion and frustration. Since provid- ing users with control over their searches increases overall satisfaction and performance, the HFG should provide users with useful features that enable users to quickly access needed information. Table 1 highlights important features that may help drive the selection of appropriate search engines. Features are organized in terms of capabilities useful 4 Table 1 Summary of CD-ROM search engine features Feature Description Search Define Sources (Advanced Search) Full-Text Search Keyword Search Boolean Search Phrase Search Index Search Wildcards Refine Searches Results Relevance Raking List of Results with Feedback Number of Hits Highlights Search Terms in Context Includes Viewer to Display Graphics Abstracts Others Customizable Features Stop Function Back Button Sequencing Results Restricts or limits the scope of the search (specific documents, chapters, entire document, etc.). Conducts searches using free-form words (text strings). Searches by specific word. Requires the establishment of “keywords.” Conducts complex logical searches that combine words using special operators (And, Or, Not). Searches for a phrase (usually enclosed in double quotation marks). Guides the search using headings and subheadings. Index linked to search. Supports use of an asterisk at the end of a word or part of a word to “match anything.” Tailors the search after the initial search is launched; refines without the need to start over. Supports a mechanism to prioritize and display results (e.g., most relevant results are shown first). Presents results in list form with a brief description of the results. Specifies the result set size. Highlights the hits (search terms) in the text. May allow user to move between instances of the words on the pages. Provides a means to view graphics as well as text results. Provides a condensed description of the document or preview documents (aids in determin- ing relevance). Searches forms and results page. Stops the search if user feels it is taking too long. Goes to previous screen. Allows user to tailor the order of presented results (grouped or sorted results).

when defining the search itself, as well as character- istics associated with displaying search results. Not only must a suitable search engine provide desirable search utilities and features, it must also be compatible with a range of user platforms and sup- port a variety of anticipated file types (PDF, HTML, word processor, database, spreadsheet, etc.). The ability to migrate from CD-ROM to web-based ap- plication is also beneficial and should be considered when designing the architecture and format of the CD-ROM. The CD-ROM provides a flexible vehicle for housing the HFG document; the medium is widely available to the user population and is capable of supporting the types of file formats and search utili- ties envisioned for the HFG document. If structured appropriately, content on the CD-ROM can also be migrated to a web-based environment if future needs demand. Another practical advantage of a CD-ROM is that it facilitates document version control; a web- based tool would be more difficult to manage revi- sions to the document. Content and Organization of the HFG The HFG needs to be streamlined and highly us- able as a day-to-day reference. The guidance por- tions need to be succinct and present only as much background as enables intelligent application of the guidelines. Human factors and systems perspectives need to be readable and useful but not encyclopedic. However, it was quite clear from the user needs workshop conducted under this project that practi- tioners find it very important to have direct access to more detailed information for times and situations where support is needed. The technical background must be easily related to specific guidelines. The willingness of an engineer to select some optimal design over a minimum specification or usual ap- proach will depend to some extent on the ability of the document to provide “backup” for that decision. For this reason, the HFG is envisioned to be a rea- sonably streamlined guidance document, but associ- ated with a related companion document or docu- ments. It is assumed that the author of any chapter of the HFG will conduct a detailed technical literature review as a basis for the development of the guide- lines. Therefore, it is assumed that these literature reviews will be available as a companion resource, even though not part of the HFG. The FHWA docu- ment, Guidelines and Recommendations to Accom- modate Older Drivers and Pedestrians, serves as a partial model for this approach. This document is es- sentially a series of guidelines with a few pages of background discussion and many individual guide- lines, each about a page or two in length. A related document, Highway Design Handbook for Older Drivers and Pedestrians, supplements the guide- lines with an extensive literature review from which the guideline recommendations were derived. This larger document is about four times the size of the smaller document. Although the HFG will neces- sarily contain much more background material than the Guidelines and Recommendations to Accommo- date Older Drivers and Pedestrians, the FHWA ex- ample illustrates the usefulness of the companion document as a means of keeping the guideline doc- ument usable. The CD-ROM format will enhance easy access to companion volumes. The proposed approach to the organization of the HFG is based on the assumption that a companion volume approach is an effective way to resolve the desire of users for a streamlined, easily searched, highly usable source of day-to-day guidance with the need for occasional access to detailed backup information and formal re- search citation and analysis. For purposes of understanding road user capa- bilities and the role of user-centered thinking in the highway safety system, it is necessary to organize some portion of the HFG around the roadway user. However, the guidelines themselves should be or- ganized around characteristics and elements of the roadway. This is more consistent with the manner in which the practitioner approaches the task and searches the document. CD-ROM capabilities for internal linking or cross-referencing need to be taken full advantage of here in order to direct the reader to relevant roadway user considerations even though the approach is through a highway design element. The recommended structure of the HFG is four major parts. The structure meets the various func- tions of the HFG and provides a meaningful basis for the approach and needs of both the traffic engi- neer and the highway designer. The structure is in- tended to be consistent with the manner in which users might approach and search the document, given their likely motivations. Each of the four parts is composed of chapters; 21 chapters are proposed for the initial HFG: • Part I: Introduction to the HFG – Chapter 1. Why Have Human Factors Guidelines for Road Systems? – Chapter 2. How to Use This Document 5

• Part II: Bringing Road User Capabilities into Highway Design and Traffic Engi- neering Practice – Chapter 3. A System Approach to Highway Safety: Thinking Like a Road User – Chapter 4. Basic Road User Capabilities • Part III: Human Factors Guidance for Roadway Location Elements – Chapter 5. From Driver Reaction Time, Ma- neuver Time, and Speed to Design Dis- tances: General Guidelines – Chapter 6. Speed Perception, Speed Choice, and Speed Control – Chapter 7. Curves (Horizontal Alignment) – Chapter 8. Grades (Vertical Alignment) – Chapter 9. Tangent Sections and Roadside (Cross Section) – Chapter 10. Transition Zones Between Varying Road Designs – Chapter 11. Non-Signalized Intersections – Chapter 12. Signalized Intersections – Chapter 13. Interchanges – Chapter 14. Construction and Work Zones – Chapter 15. Rail–Highway Grade Crossings – Chapter 16. Special Considerations for Urban Environments – Chapter 17. Special Considerations for Rural Environments • Part IV: Human Factors Guidance for Traffic Engineering Elements – Chapter 18. Signing – Chapter 19. Changeable Message Signs – Chapter 20. Markings – Chapter 21. Lighting While not exhaustive, these chapters would be reasonably comprehensive and provide an effective aid to designers and traffic engineers. Part I is introductory and intentionally brief, with two short chapters. The purpose of the first chapter is to describe the needs for the HFG and the purposes it is intended to serve. It will define “human factors” and their role in design and safety in high-level terms (Part II will provide greater de- tail). The chapter will clarify the relationship of the HFG to other design guides and reference sources and explain its role as a complement to primary stan- dards and engineering guides. The second chapter of Part I will explain to the reader how to use the HFG. It will describe the organization and will detail the automated search capabilities. The availability and role of the companion literature review papers will be explained. The relationship to other sources of guidance will be described, and the system of cross- referencing within the HFG will be discussed. A set of references to other resource materials will be pro- vided, with a capsule description of how each relates to the HFG. A shortcoming of other traffic engi- neering reference documents that have been pro- duced as CD-ROM or web-based versions is that search capabilities and how to use them are not made evident. Users may not be aware of what func- tions they have available or exactly how these func- tions work. For example, there may be Boolean functions that permit a more refined search (using an “and” function) or the ability to screen many irrele- vant “hits” (using a “not” function). Yet the docu- ment has no description or link to such information. The clarification of how the document can be effec- tively searched should be an important part of Chap- ter 2. Overall, then, the intent of Part I is simply to provide a succinct basis for use of the HFG: what it is and how it works. Part II deals with road user capabilities and the role of road user–centered thinking in the systems conception of highway safety. Part II is composed of two chapters. The initial chapter introduces the sys- tem approach and emphasizes “thinking like a road user.” It is meant to be a very readable chapter, with- out a lot of jargon, models, or data. One of the real issues for the HFG is how to motivate a practitioner to read it, other than in a very specific problem- solving mode. The HFG should be able to influence the thinking of the traffic engineer, and maybe even more importantly the highway designer, so that they adopt a more global, systems view and the ability to incorporate road user needs into their approach. This chapter is where to accomplish this. While there is no means of forcing someone to read any portion of the HFG, this chapter will be designed to be inviting and readable. It should use “punchy,” succinct text and make maximum use of the multimedia capabil- ities of CD-ROM. For example, these capabilities might include driver’s eye view video clips, anima- tions, dynamic graphics, side-by-side comparisons, and so forth. The chapter will include a section on “thinking like a road user” that will introduce a few key concepts and issues in a very practical, jargon- free manner. The second chapter within Part II de- fines and quantifies basic driver capabilities directly related to engineering practice and decision making. 6

It explains fundamental behavioral factors, such as perception-reaction time and expectancy. It pro- vides basic empirical data on human perception and performance characteristics. While many readers may not read this chapter beginning to end, it will serve as an essential link to later guidelines and prin- ciples and can be cross-referenced as needed. Parts III and IV are related in that they provide the set of specific guidelines, organized around fac- tors relevant to the designer or traffic engineer. These parts are the core of the HFG for practical use. The Project 17-18(8) analysis, strongly confirmed in the user workshop, was that the guidelines should be organized around the primary types of roadway lo- cations, but while this is desirable, it is not suffi- cient. Many of the guidance principles are not loca- tion specific and would be redundant to consider within each chapter. Furthermore, the user may con- ceive of his or her issue in terms of a device or other engineering element and seek guidance with respect to human-centered principles for the device. There- fore, the guidelines are organized under two distinct parts: Human Factors Guidance for Roadway Loca- tion Elements and Human Factors Guidance for Traffic Engineering Elements. Cross-referencing and links between these sections are assumed and remain critical for steering the user to all appropri- ate guidance without an unduly redundant and un- wieldy document. Part III organizes the guidelines with respect to some type of roadway location, such as a “signalized intersection” or a “construction and work zone.” Part IV then presents a range of cross- cutting issues that relate to traffic engineering ele- ments (e.g., signs and lighting). Chapter Structure and Features The guideline chapters (under Parts III and IV) should share a common format and a common ap- proach to presenting the issues and guidance. As the HFG is developed, different authors will be respon- sible for the various chapters. The individual authors, as topic experts, will have to determine for their chapter precisely what the specific guideline needs are. However, a common format will aid the user and may help ensure a comprehensive treatment. The core of each chapter in Parts III and IV is a set of guideline statements. Although the guidelines are the major component, there are other sections important to the standard chapter structure. As noted in the previous section, it is assumed that for each chapter there will have been a literature review con- ducted. The detailed information and citations in that review do not need to be included in the body of the chapter in the HFG, but a link to the full review is necessary. However, each chapter should begin with a brief background section that puts the safety and driver-centered issues in context. This back- ground should highlight the major types of design and operational issues that tend to occur, the nature of the safety problem (i.e., the crash characteristics), road users that may have special needs (e.g., heavy trucks and pedestrians), and the major human factor issues. If kept brief (e.g., 2 pages), this background section will more likely be read. The background section provides the opportunity for the chapter au- thor to set a context in which the specific guidelines will be more understandable and appreciated. An additional section is suggested for the chap- ters of Parts III and IV. This was a “Road User Re- quirements Analysis” that maps human factors needs and strategies in a systematic manner, using headings of • Required acts, • Driver information requirements, • Driver action requirements and decisions, • Contributing factors, and • Addressing potential solutions. In previous projects, this sort of analysis proved to be both a very useful tool for developing recom- mendations and an effective means of communicat- ing the human factors needs and strategies to an au- dience without human factors expertise. However, the issues of the sample chapter did not lend them- selves readily to this format, and for many planned chapters, the range of issues may simply be too great to employ this technique. Therefore, it is suggested that HFG chapter authors consider a tabular format User Requirements Analysis as a possible feature for a given chapter. However, this need not be a standard part of all chapters. The project team also considered the inclusion of a decision tree or some other type of diagnostic scheme as an element of each chapter. Such a tool might prove valuable to the practitioner. While the development of diagnostic tools may be beyond the scope of the basic HFG development effort for many topics, it may be appropriate for others. For exam- ple, in the sample chapter, the inclusion of a diag- nostic procedure was helpful. Therefore, this should be a chapter-by-chapter decision. It has been rec- 7

ommended that NCHRP or other agencies give seri- ous consideration to parallel development of diag- nostic tools and other decision aids that might com- plement HFG chapters. This would allow more thorough development and validation than might be possible within a limited chapter-writing effort. The project team, in discussing the details of the chapter structures in Parts III and IV, concluded that NCHRP Project 17-18(8) should not overly specify the organization and specific set of guidelines to be included in the chapter. That is exactly what the au- thors must do using their expertise, the literature re- view, and the systematic road user requirements analysis. Also, the relevant TRB technical commit- tees should coordinate with chapter authors to pro- vide input to the needed set of guidelines. The struc- ture of the initial portions of a chapter will help clarify an organization for the individual guidance items and help make more evident where a guideline is required. As noted earlier, the HFG need not try to comprehensively address every aspect of design and operations, which would be redundant with other guides and would result in a voluminous set of guidelines. The guidelines in each chapter should be 8 developed based on a perceived need. Issues are treated by exception or where there are combina- tions of elements or other concerns not adequately dealt with in other sources. REPORT AVAILABILITY The complete report for NCHRP Project 17- 18(8) is available on TRB’s website as NCHRP Web Document 70. ACKNOWLEDGMENTS This study was conducted under NCHRP Proj- ect 17-18(8), “Comprehensive Human Factors Guidelines for Road Systems.” It was guided by NCHRP Panel 17-18, chaired by Mr. Thomas E. Bryer, with members Mr. Jesse Bhullar, Dr. Leanna Depue, Ms. Barbara Harsha, Mr. Bruce Ibarguen, Ms. Marlene Markison, Ms. Margaret Moore, Ms. Kim F. Nystrom, Mr. Peter F. Rusch, Mr. Rudy Umbs, Mr. Anthony D. Wyatt, Dr. Ray Krammes, Dr. Jesse Blatt, Mr. Ken Kobetsky, and Dr. Richard Pain.

These digests are issued in order to increase awareness of research results emanating from projects in the Cooperative Research Programs (CRP). Persons wanting to pursue the project subject matter in greater depth should contact the CRP Staff, Transportation Research Board of the National Academies, 500 Fifth Street, NW, Washington, DC 20001. Transportation Research Board 500 Fifth Street, NW Washington, DC 20001