Guide for the Geometric Design of Driveways (2010)

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Purpose and Scope of the Guide This document contains guidelines for the geometric design of driveways. The guidelines are an outgrowth of a literature review and synthesis, a survey of state DOTS, and field studies that were a part of NCHRP Project 15-35, “Geometric Design of Driveways.” This publication com- plements documents such as the AASHTO Policy on the Geometric Design of Streets and High- ways (1-1) and the Access Management Manual (1-2). This guide is intended for use in both the public and private sectors. The following driveway design objectives guided the authors during the preparation of this guide: • Provide a safe environment for various users: bicyclists, motorists, and pedestrians (includ- ing pedestrians with disabilities and transit passengers). • Provide geometry that accommodates the characteristics and limitations of the various users, and avoid geometric conditions that create traffic operations problems. • Provide driveways that allow traffic to flow smoothly. • Avoid driveway locations that create traffic operations problems. • Provide driveways that are conspicuous and clearly delineated for the various users. Although it may be impossible to perfectly achieve these objectives, some designs come much closer than others in achieving these objectives. Every driveway connection creates an intersection, which creates conflicts with bicyclists, pedestrians, and other motor vehicles. An objective of good design is to seek a balance that minimizes the actual conflicts and accommodates the demands for travel and access. Driveways can be defined as private roads that provide access between public ways and activ- ities or buildings on abutting land (1-3). However, when roadway designers use the term “drive- way,” they are often referring to just a part of a driveway—the area where the driveway intersects the public highway or street. With few exceptions, the contents of this guide reflect the roadway designer definition of driveway and do not address the design of a driveway well within a private site, except as such design affects the driveway intersection with the public roadway. Many of these recommendations were prepared to address access connections that are designed to look more like the typical driveway rather than those looking like public roadways. Need for This Guide Driveways are integral to the roadway-based transportation system. They are found along most roadways throughout urban, suburban, and rural areas. They range from single-lane connections serving single-family residences to multilane, divided-access connections to major activity centers. 1 C H A P T E R 1 Introduction

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. 2 Guide for the Geometric Design of Driveways (a) (b) Exhibit 1-1. The consequences of driveway design decisions.

• Chapter 5 sets forth various geometric design elements. These include plan and cross sections, driveway length, vertical alignment, and related elements. Material related to and supporting the contents of this publication, including an extensive review of literature, can be found in NCHRP Web-Only Document 151: Geometric Design of Driveways. References 1-1. AASHTO. A Policy on Geometric Design of Highways and Streets. Washington, DC (2004) 896 pp. 1-2. TRB Committee on Access Management. Access Management Manual. Transportation Research Board, National Research Council, Washington, DC (2003) 373 pp. 1-3. Webster’s Collegiate Dictionary. G&C Merriam Company, Springfield, MA (1981). 1-4. Rawlings, J., and Gattis, J. L. “Detailed Study of Driveway Collision Patterns in an Urban Area.” Compendium of Papers, 87th Annual Meeting, Transportation Research Board, National Research Council, Washington, DC (2008). 1-5. AASHO. An Informational Guide for Preparing Private Driveway Regulations for Major Highways. Washington, DC (October 10, 1959, copyright 1960) 31 pp. 1-6. ITE. Guidelines for Driveway Location and Design. Washington, DC (1987) 23 pp. 1-7. U.S. Access Board. Accessible Public Rights of Way: Design Guide. U.S. Architectural and Transportation Barriers Compliance Board, Washington, DC (1999). Introduction 3