National Academies Press: OpenBook
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2014. Superelevation Criteria for Sharp Horizontal Curves on Steep Grades. Washington, DC: The National Academies Press. doi: 10.17226/22312.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2014. Superelevation Criteria for Sharp Horizontal Curves on Steep Grades. Washington, DC: The National Academies Press. doi: 10.17226/22312.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2014. Superelevation Criteria for Sharp Horizontal Curves on Steep Grades. Washington, DC: The National Academies Press. doi: 10.17226/22312.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2014. Superelevation Criteria for Sharp Horizontal Curves on Steep Grades. Washington, DC: The National Academies Press. doi: 10.17226/22312.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2014. Superelevation Criteria for Sharp Horizontal Curves on Steep Grades. Washington, DC: The National Academies Press. doi: 10.17226/22312.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2014. Superelevation Criteria for Sharp Horizontal Curves on Steep Grades. Washington, DC: The National Academies Press. doi: 10.17226/22312.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2014. Superelevation Criteria for Sharp Horizontal Curves on Steep Grades. Washington, DC: The National Academies Press. doi: 10.17226/22312.
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Below is the uncorrected machine-read text of this chapter, intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text of each book. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

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 774 Superelevation Criteria for Sharp Horizontal Curves on Steep Grades Darren J. Torbic Mitchell K. O’Laughlin Douglas W. Harwood Karin M. Bauer Courtney D. Bokenkroger Lindsay M. Lucas John R. Ronchetto MRIGlobal Kansas City, MO Sean Brennan Eric Donnell Alexander Brown Tejas Varunjikar ThoMas D. laRson PennsylvanIa TRansPoRTaTIon InsTITuTe aT The PennsylvanIa sTaTe unIveRsITy University Park, PA Subscriber Categories Design • Operations and Traffic Management • Safety and Human Factors 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 Board’s 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 774 Project 15-39 ISSN 0077-5614 ISBN 978-0-309-30790-1 Library of Congress Control Number 2014946500 © 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 manufacturers’ 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 Academy’s 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 Board’s 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 AUTHOR ACKNOWLEDGMENTS This report was prepared by Dr. Darren J. Torbic, Mr. Douglas W. Harwood, Ms. Karin M. Bauer, Ms. Lindsay M. Lucas, and Mr. John R. Ronchetto of MRIGlobal; Dr. Sean Brennan, Dr. Eric Donnell, and Mr. Alexander Brown of the Thomas D. Larson Pennsylvania Transportation Institute at the Pennsylvania State University; Mr. Mitchell K. O’Laughlin of Kiewit (formerly of MRIGlobal); Ms. Courtney D. Boken- kroger of Elanco (formerly of MRIGlobal); and Mr. Tejas Varunjikar of Nexteer Automotive (formerly of the Thomas D. Larson Pennsylvania Transportation Institute at the Pennsylvania State University). The authors wish to thank the state departments of transportation of California, Maryland, Pennsylvania, Washington, and West Virginia for their assistance in this research. CRP STAFF FOR NCHRP REPORT 774 Christopher W. Jenks, Director, Cooperative Research Programs Christopher Hedges, Manager, National Cooperative Highway Research Program David A. Reynaud, Senior Program Officer Megan A. Chamberlain, Senior Program Assistant Eileen P. Delaney, Director of Publications Natalie Barnes, Senior Editor NCHRP PROJECT 15-39 PANEL Field of Design—Area of General Design Norman H. Roush, West Virginia DOT (retired), Racine, OH (Chair) Kenneth T. Briggs, KCI Technologies Inc., Sparks, MD Antonette C. Clark, California DOT, Sacramento, CA James R. Kladianos, Wyoming DOT, Laramie, WY John Roccanova, California DOT, Stockton, CA Larry F. Sutherland, Parsons Brinckerhoff, Columbus, OH Jeffrey Shaw, FHWA Liaison Stephen F. Maher, TRB Liaison

F O R E W O R D By David A. Reynaud Staff Officer Transportation Research Board This report provides superelevation criteria for horizontal curves on steep grades. A series of field studies and vehicle dynamics simulations were undertaken to investigate combina- tions of horizontal curve and vertical grade design. The report should be of interest to state and local highway design practitioners. Sharp, horizontal curves on steep downgrades represent a potential safety concern for vehicles, especially heavy vehicles. Examples where this combination may occur are inter- change ramp movements, curves on mountainous roads, or high-speed downgrade curves on controlled-access roadways. At these locations, the complicating factors of grade, pave- ment cross slope, and pavement friction fully tax the driver’s ability to provide correct vehicle positioning without compromising control of the vehicle. Superelevation criteria, horizontal curvature, and other associated geometric criteria needed to be developed for situations where steep grades are located on sharp horizontal curves. The objective of NCHRP Project 15-39 was to develop superelevation criteria for hori- zontal curves on steep grades. Other criteria associated with design of horizontal curves (e.g., tangent-to-curve transitions, spiral transitions, lateral shift of vehicles traversing the curve, need for pavement widening, and determination of curve radii) were also considered. The research was performed by MRIGlobal and the Pennsylvania State University. Design criteria were developed based on a series of field studies and vehicle dynamic simulations. Field studies were conducted to collect vehicle speed and lane-changing maneuver data from locations across the United States, as well as representative samples of tire–pavement friction data for various pavement surface conditions. Vehicle dynamic simulations used AASHTO design criteria in combination with field-measured data. Three classes of pas- senger vehicles and three classes of trucks were considered for safety analysis. The report provides design guidance based on the analyses for sharp horizontal curves on steep grades.

C O N T E N T S 1 Summary 7 Section 1 Introduction 7 1.1 Background 8 1.2 Research Objective and Scope 8 1.3 Overview of Research Methodology 8 1.4 Key Terms 9 1.5 Outline of Report 10 Section 2 Literature Review 10 2.1 Horizontal Curve Design 14 2.2 Heavy Trucks 14 2.3 Driver Comfort 14 2.4 Friction Studies 16 2.5 Vehicle Dynamics Models 18 2.6 Current Practice 20 Section 3 Field Studies 20 3.1 Site Selection 21 3.2 Speed and Vehicle Maneuver Studies 31 3.3 Instrumented Vehicle Studies 36 3.4 Friction Testing 40 Section 4 Analytical and Simulation Modeling 40 4.1 Analysis Approach 43 4.2 Step 1: Define Basic Tire–Pavement Interaction Model(s) and Estimate Lateral Friction Margins against Skidding in AASHTO’s Current Horizontal Curve Policy 49 4.3 Step 2: Define Road Geometries and Variable Ranges for Use in Subsequent Steps 50 4.4 Step 3: Develop Side Friction Demand Curves and Calculate Lateral Friction Margins against Skidding Considering Grade Using the Modified Point-Mass Model 53 4.5 Step 4: Define Vehicles and Maneuvers to Use in Non-Point-Mass Models 55 4.6 Step 5: Predict Wheel Lift Using Quasi-static Models 58 4.7 Step 6: Predict Skidding of Individual Axles during Steady-State Behavior on a Curve 65 4.8 Step 7: Predict Skidding of Individual Axles during Braking and Lane-Change Maneuvers on a Curve 98 4.9 Step 8: Predict Skidding of Individual Axles during Transient Steering Maneuvers and Severe Braking 110 4.10 Step 9: Predict Skidding of Individual Wheels 139 4.11 Step 10: Predict Wheel Lift of Individual Wheels during Transient Maneuvers

143 4.12 Step 11: Analysis of Upgrades 155 4.13 Summary of Analytical and Simulation Modeling 157 Section 5 Crash Analysis 157 5.1 Data Description 159 5.2 Analysis Approach 159 5.3 Analysis Results 162 Section 6 Conclusions, Geometric Design Guidance, and Future Research 162 6.1 General Conclusions 164 6.2 Geometric Design Guidance 165 6.3 Future Research 167 References A-1 Appendix A Nomenclature B-1 Appendix B Vehicle Parameters Used in Simulation C-1 Appendix C Potential Changes Recommended for Consideration in the Next Editions of the Green Book and MUTCD Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions.

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TRB’s National Cooperative Highway Research Program (NCHRP) Report 774 provides superelevation criteria for horizontal curves on steep grades. A series of field studies and vehicle dynamics simulations were undertaken to investigate combinations of horizontal curve and vertical grade design.

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