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2 Guide for the Geometric Design of Driveways Exhibit 1-1. The consequences of driveway design decisions. (a) (b) Driveways vary in size and design according to the activities they serve and the associated traf- fic volumes, development densities, proximity to intersections, and exposure to bicyclists and pedestrians. The design and appearance of driveways have evolved over the years as technolo- gies and land development patterns have changed. Both anecdotal experience and structured research studies show that certain driveway design practices create problems for bicyclists, motorists, and pedestrians. Studies have found that any- where from 11 to 19% of all reported urban traffic collisions involve a driveway (1-4). The loca- tion and design of a driveway affect both traffic flow and safety on both the driveway and on the adjacent public roadway. There has been less study of driveways than of many other types of roadway facilities. Among the few publications that have addressed driveway design are the following: · The American Association of State Highway Officials' (AASHO) guidelines published in 1959 (1-5), · The Institute of Transportation Engineers (ITE) guidelines published in 1987 (1-6), · Technical assistance from the U.S. Access Board published in 1999 (1-7), and · The TRB Access Management Manual (1-2). The growing emphasis on multi-modal transportation and the requirements of the Americans with Disabilities Act (ADA) also call for a re-examination of driveway design practices. During preparation of this document, it became apparent that structured studies and documented infor- mation on which to base recommendations is often limited. It is hoped that future research will help improve the knowledge base. Exhibit 1-1 illustrates some of the operational and safety problems that can arise when drive- way designs are inadequate. Organization and Structure of the Guide This guide consists of the following chapters: · Chapter 2 lists terms and definitions. · Chapter 3 discusses some of the basic geometric design controls. These controls include basic characteristics of users and vehicles, as well as site-specific controls, such as setting and land use, types of users, vehicle types, volumes, and speeds. These considerations affect the design practices recommended in the following chapters. · Chapter 4 briefly mentions access spacing principles and guidelines and references other pub- lications for more information.