The increasing numbers and percentages of aging persons using our nation's streets and highways in the decades ahead will pose many challenges to transportation engineers who focus on safety and operational efficiency. According to the Administration on Aging, the 65-and-older age group, which numbered 39.6 million in the United States in 2009, will grow to more than 55 million in 2020. By 2030, there will be approximately 72.1 million aging persons, accounting for roughly one-fifth of the population of driving age in this country. In effect, for many aspects of road planning and design, the "design driver" and the "design pedestrian" of the early 21st century will likely be 65 or over.

There are important consequences of these changing demographics, and life for aging persons depends to an extraordinary degree on remaining independent. Independence requires mobility. In our society the overwhelming choice of mobility options is the personal automobile. Other mobility options that may be utilized include public transit and walking. This means that there will be a steadily increasing proportion of drivers and pedestrians who experience declining vision; slowed decision-making and reaction times; exaggerated difficulty when dividing attention between traffic demands and other important sources of information; and reductions in strength, flexibility, and general fitness.

In a proactive response to this pending surge in aging road users, the Federal Highway Administration (FHWA) published the Older Driver Highway Design Handbook in 1998. The 1998 Handbook provided highway designers and engineers with the first practical information source linking age-related declines in functional capabilities to enhanced design, operational, and traffic engineering treatments, keyed to specific roadway features. Experience with these enhanced treatments, including extensive feedback from local and State-level practitioners, led to the release of the Highway Design Handbook for Older Drivers and Pedestrians in 2001. Now, a third edition of this resource has been prepared, under a new title, which incorporates new research, expands the range of applications covered by the Handbook, and introduces format changes—including a web based version—that will facilitate access and use by engineering professionals to improve our streets and highways in the years ahead.

Part I of this Handbook retains its focus on five broad categories of roadway features, each containing a number of specific design elements for which guidance is presented. The top priority is intersections, reflecting aging drivers' most serious and enduring crash problem area, as well as the greatest exposure to risk for pedestrians. Next, well documented difficulties with merging/weaving and lane changing maneuvers focus attention on interchanges. Roadway segments, with an emphasis on curves and passing zones, plus highway construction/work zones, are included due to heightened tracking (steering) demands that may increase a driver's workload along with an increased potential for unexpected events that require a rapid response. Finally, highway-rail grade crossings merit consideration as sites where conflicts are rare, and thus unexpected, and where problems of detection (with passive controls) may be exaggerated due to sensory losses with advancing age.

The treatments presented in Part I are followed by a more lengthy section, Part II, presenting the rationale and supporting evidence. Within each of these two major Handbook sections, material is organized in terms of five subsections, corresponding to the categories of roadway features noted above. Preceding the treatments, a chapter titled "How To Use This Handbook" explains codes used throughout the document to cross-reference the Manual on Uniform Traffic Control Devices (MUTCD), A Policy on Geometric Design of Highways and Streets (the Green Book) and other manuals and guides. In addition, a guide for interpreting graphics used in the Handbook and a table for translating speeds and distances into "preview times" for driver decision and response selection are presented; and, a structured approach to help engineering professionals decide when to implement Handbook treatments is described. A supplementary discussion about how to determine the visibility of roadway elements is appended to this edition of the Handbook. The Handbook concludes with a glossary providing definitions of selected terms and a reference list.

Most of the treatments in this Handbook are based on supporting evidence drawn from a comprehensive review of field and laboratory research addressing human factors and highway safety. The supporting information presented in Part II represents the latest relevant information and data available to the authors at the time the document was assembled. Some research findings have been carried forward from previous Handbooks, while other findings are new since the release of the 2001 Handbook. A number of additional treatments were considered but ultimately dropped or deferred because of gaps or deficiencies in the supporting studies. This edition also includes some "Promising Practices"—treatments that are being used by one or more agencies, which although they have not been evaluated formally, are generally believed to benefit the aging population of roadway users based on subjective assessment by the staff participating in the development of this Handbook. This conservative approach also dictated that the Handbook's treatments relate to the demonstrated performance deficits of normally aging drivers and pedestrians. It deserves mention that diminished capabilities that result from the onset of Alzheimer's disease and related dementias, which may afflict over 10 percent of those age 65 and older and over 40 percent of those age 85 and older, are not explicitly targeted in these guidelines. Neither are the compromises in performance that are associated with drowsiness, fatigue or distraction.

This resource can be applied preemptively to enhance safety wherever there are aging road users in a given jurisdiction, or it may be employed primarily as a "problem solver" at crash sites. The implementation of these treatments will translate into real gains in safety and mobility for our nation's aging citizens, and indeed for all users of our surface transportation system. Readers of this Handbook must note, however, that the treatments presented in this Handbook do not constitute a new standard of required practice. The final decision about when and where to apply the treatments presented in this Handbook remains at the discretion of State and local design and engineering professionals.