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N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 783 Evaluation of the 13 Controlling Criteria for Geometric Design Douglas W. Harwood Jessica M. Hutton Chris Fees Karin M. Bauer Alan Glen Heidi Ouren MRIGlobal Kansas City, MO Quincy Engineering Sacramento, CA HQE, Inc. Oakland, CA Subscriber Categories Design TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2014 www.TRB.org Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration
NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States Department of Transportation. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Boardâs recognized objectivity and understanding of modern research practices. The Board is uniquely suited for this purpose as it maintains an extensive committee structure from which authorities on any highway transportation subject may be drawn; it possesses avenues of communications and cooperation with federal, state and local governmental agencies, universities, and industry; its relationship to the National Research Council is an insurance of objectivity; it maintains a full-time research correlation staff of specialists in highway transportation matters to bring the findings of research directly to those who are in a position to use them. The program is developed on the basis of research needs identified by chief administrators of the highway and transportation departments and by committees of AASHTO. Each year, specific areas of research needs to be included in the program are proposed to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America NCHRP REPORT 783 Project 17-53 ISSN 0077-5614 ISBN 978-0-309-30796-3 Library of Congress Control Number 2014948497 Â© 2014 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. Permission is given with the understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA, FMCSA, FTA, or Transit Development Corporation endorsement of a particular product, method, or practice. It is expected that those reproducing the material in this document for educational and not-for-profit uses will give appropriate acknowledgment of the source of any reprinted or reproduced material. For other uses of the material, request permission from CRP. NOTICE The project that is the subject of this report was a part of the National Cooperative Highway Research Program, conducted by the Transportation Research Board with the approval of the Governing Board of the National Research Council. The members of the technical panel selected to monitor this project and to review this report were chosen for their special competencies and with regard for appropriate balance. The report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the Governing Board of the National Research Council. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board, the National Research Council, or the program sponsors. The Transportation Research Board of the National Academies, the National Research Council, and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturersâ names appear herein solely because they are considered essential to the object of the report.
The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished scholars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. Upon the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and technical matters. Dr. Ralph J. Cicerone is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Academy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achievements of engineers. Dr. C. D. Mote, Jr., is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, upon its own initiative, to identify issues of medical care, research, and education. Dr. Victor J. Dzau is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academyâs purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Academy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both Academies and the Institute of Medicine. Dr. Ralph J. Cicerone and Dr. C. D. Mote, Jr., are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is one of six major divisions of the National Research Council. The mission of the Transporta- tion Research Board is to provide leadership in transportation innovation and progress through research and information exchange, conducted within a setting that is objective, interdisciplinary, and multimodal. The Boardâs varied activities annually engage about 7,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individu- als interested in the development of transportation. www.TRB.org www.national-academies.org
C O O P E R A T I V E R E S E A R C H P R O G R A M S CRP STAFF FOR NCHRP REPORT 783 Christopher W. Jenks, Director, Cooperative Research Programs Christopher Hedges, Manager, National Cooperative Highway Research Program B. Ray Derr, Senior Program Officer AndrÃ©a Parker, Senior Program Assistant Eileen P. Delaney, Director of Publications Ellen M. Chafee, Editor NCHRP PROJECT 17-53 PANEL Field of TrafficâArea of Safety Terry L. Berends, Washington State DOT, Wenatchee, WA (Chair) Mark A. Marek, Texas DOT, Austin, TX Troy A. Jerman, Iowa DOT, Atlantic, IA In-Kyu âQâ Lim, Virginia DOT, Richmond, VA Paul F. Schneider, New Jersey DOT, Trenton, NJ Xiaoduan Sun, University of Louisiana at Lafayette, Lafayette, LA William C. Taylor, Michigan State University, East Lansing, MI Mark Doctor, FHWA Liaison Bernardo Kleiner, TRB Liaison
F O R E W O R D By B. Ray Derr Staff Officer Transportation Research Board This report describes the impact of the controlling roadway design criteria on safety and operations for urban and rural roads. This information will be useful to geometric designers and those responsible for reviewing designs, particularly in agencies that are transitioning away from âstandards-based design.â In 1985, the FHWA designated 13 specific design elements as controlling criteria for roadway design (see Mitigation Strategies for Design Exceptions). The 13 controlling criteria are (1) design speed, (2) lane width, (3) shoulder width, (4) bridge width, (5) structural capacity, (6) horizontal alignment, (7) vertical alignment, (8) grade, (9) stopping sight dis- tance, (10) cross slope, (11) superelevation, (12) vertical clearance, and (13) horizontal clearance. Federally assisted highway construction and reconstruction projects must meet the established design criteria for these elements, or a formal design exception must be pre- pared and approved. Different procedures apply to rehabilitation projects, but these design elements are still key considerations in design. Since their designation, the 13 controlling criteria and their application have not been reconsidered as new knowledge has been gained about the relationships between geometric design elements and safety and operations. In NCHRP Project 17-53, MRIGlobal and their subcontractors (Quincy Engineering and HQE, Inc.) investigated what is known about the safety and operational effects of the 13 controlling and other important geometric design criteria. Several small studies were done to augment the information found in the literature. This information was used to assess the sensitivity of safety and operations to design decisions for these criteria for different types of roads. The research also addressed how to reduce confusion related to the definitions of the controlling criteria. The use of the controlling criteria in design exception processes was also explored, including through interviews with state department of transportation (DOT) personnel. It is expected that the report will be useful to state DOTs in reviewing their design exception policies for non-federal projects.
C O N T E N T S 1 Summary 3 Section 1 Introduction 3 1.1 Background 4 1.2 Research Objectives and Scope 4 1.3 Organization of NCHRP Report 783 5 Section 2 Design Criteria, Traffic Operational and Safety Effects, and Mitigation Strategies for the 13 Controlling Criteria 5 2.1 Design Speed 7 2.2 Lane Width 14 2.3 Shoulder Width 18 2.4 Bridge Width 20 2.5 Structural Capacity 20 2.6 Horizontal Alignment 24 2.7 Vertical Alignment 28 2.8 Grade 35 2.9 Stopping Sight Distance 36 2.10 Cross Slope 37 2.11 Superelevation 37 2.12 Vertical Clearance 38 2.13 Horizontal Clearance/Lateral Offset 39 2.14 Summary of Traffic Operational Effects 39 2.15 Summary of Traffic Safety Effects 42 Section 3 Design Exception Practices 42 3.1 Published Reviews of Design Exception Practices 44 3.2 Interviews with State Highway Agency Staff 49 Section 4 Expanded Traffic Operational and Safety Knowledge Concerning the 13 Controlling Criteria 49 4.1 Operational Effects of Lane Width on Urban and Suburban Arterials 50 4.2 Safety Effects of Lane Width on Urban and Suburban Arterials 51 4.3 Safety Effects of Bridge Width on Rural Two-Lane Highways 52 4.4 Operational Effects of Horizontal Alignment on Rural Multilane Divided Highways and Urban and Suburban Arterials 54 4.5 Safety Effects of Horizontal Alignment on Rural Freeways and Rural Multilane Highways 56 4.6 Safety Effect of Vertical Alignment on Rural Multilane Divided Highways 58 4.7 Safety Effects of Stopping Sight Distance at Crest Vertical Curves on Rural Two-Lane Highways
62 Section 5 Refinement of Definitions for the 13 Controlling Criteria 62 5.1 Refinement of Criteria Definitions 66 5.2 Suggested Renaming of the 13 Controlling Criteria 67 5.3 Other Potential Controlling Criteria for Design 68 Section 6 Prioritization of the 13 Controlling Criteria 68 6.1 Ranking of the 13 Controlling Criteria from NCHRP Synthesis 417 69 6.2 Sensitivity Analysis of Key Controlling Criteria for Specific Roadway Types 79 6.3 Priorities for the Controlling Criteria 81 Section 7 Interpretation of Results 82 7.1 Shoulder Width 82 7.2 Lane Width 82 7.3 Horizontal Curve Radius 83 7.4 Superelevation 83 7.5 Grade 83 7.6 Stopping Sight Distance 84 7.7 Bridge Width 84 7.8 Cross Slope 85 7.9 Sag Vertical Curve Length 85 7.10 Horizontal Clearance/Lateral Offset 85 7.11 Summary of Results for Rural Two-Lane Highways, Rural Multilane Highways, and Rural and Urban Freeways 85 7.12 Summary of Results for Urban and Suburban Arterials 86 Section 8 Conclusions and Recommendations 86 8.1 Conclusions 87 8.2 Recommendations 90 References