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Introduction P A R T I
1.1 Purpose of Human Factors Guidelines for Road Systems The purpose of Human Factors Guidelines for Road Systems (HFG) is to provide the best fac- tual information and insight on the characteristics of road users to facilitate safe roadway design and operational decisions. A number of existing guides, standards, and references are available to facilitate safe roadway design and operational decisions, including A Policy on Geometric Design of Highways and Streets (AASHTO, 2011), the Manual on Uniform Traffic Control Devices (MUTCD) (FHWA, 2009), and the Highway Safety Manual (HSM) (AASHTO, 2010). However, these materials often lack a substantive presentation and discussion of human factor 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 integra- tion of three componentsâthe roadway, the vehicle, and the roadway userâthe 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 do not pro- vide highway designers and traffic engineers with adequate guidance for incorporating road user needs, limitations, and capabilities when dealing with design and operational issues. The Human Factors Guidelines for Road Systems is intended to provide human factors princi- ples 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 road userâs capabilities and limita- tions into the practice of design, operations, and safety. The HFG 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 safely usable by the broad range of road users. 1.2 Overview of the HFG This document provides practitioners who design and operate streets and highways with relevant human factors data and principles, in a useful guideline form. The ITE Traffic Engi- neering Handbook (Pline, 1999) cites a definition of âtraffic engineeringâ as âthat 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.â Thus the discipline of human factors is recognized as an integral contrib- utor to traffic engineering practice. Many highway designers and traffic engineers, however, 1-1 C H A P T E R 1 Why Have Human Factors Guidelines for Road Systems?
do not have a clear understanding of what human factors is and how its principles are relevant to their work. Human factors is an applied, scientific discipline that tries to enhance the relationship between devices and systems, and the people who are meant to use them. As a discipline, human factors approaches system design with the âuserâ as its focal point. Human factors practitioners bring expert knowledge concerning the capabilities and limitations of human beings that are impor- tant for the design of devices and systems of many kinds. There has been a number of elements within the field of transportation engineering that have benefited from human factors research, including sight distance requirements; work zone layouts; sign design, placement, and spac- ing criteria; dimensions for road markings; color specifications; sign letter fonts and icons; and signal timing. Basic crash statistics in the United States highlight the importance of human factors to road system design. In 2001, for example, there were more than 6 million police-reported (and many more non-reported) collisions in the United States, with attendant loss of life, property, and pro- ductivity (NHTSA, 2002). Furthermore, some form of driver error was usually a contributing factor in nearly half (approximately 44%) of the crashes leading to a fatality. âErrorâ 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. While many roadway design practices are based on extensive, well-documented, and fully appropriate behavioral data, this is not always the case. Some design practices recommended by existing standards and guidance can include the following limitations: â¢ They do not have any empirical basis and/or have not been formally evaluated for adequacy for road users. â¢ They are based on outdated data that may no longer be representative of current driver behaviors. â¢ They are based on overly simple models of what road users see or do. â¢ They are based on incorrect assumptions about road usersâ capabilities and limitations. â¢ They do not reflect recent changes in communications technology, vehicle features, roadway features, roadside environment, traffic control devices, or traffic operational characteristics. â¢ They do not reflect the special needs of some road users, such as older drivers, visually impaired pedestrians, pedestrians with mobility limitations, heavy truck operators, and users of lower-speed alternative transportation devices. â¢ They do not adequately address trade-offs between conflicting demands that are related to important road user characteristics. â¢ They may not address specific combinations of roadway design features that can have an impact on road user behavior and subsequent safety. The HFG provides guidance based on empirical data and expert judgment without the above limitations. HFG WHY HAVE HUMAN FACTORS GUIDELINES? Version 2.0 1-2