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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 730 Design Guidance for Freeway Mainline Ramp Terminals Darren J. Torbic Jessica M. Hutton Courtney D. Bokenkroger Douglas W. Harwood David K. Gilmore Melanie M. Knoshaug John J. Ronchetto MRIGlobal Kansas City, MO Marcus A. Brewer Kay Fitzpatrick Susan T. Chrysler Jesse Stanley Texas a&M TRanspoRTaTIon InsTITuTe College Station, TX Subscriber Categories Highwaysâ â¢â Design TRANSPORTAT ION RESEARCH BOARD WASHINGTON,âD.C. 2012 www.TRB.orgâ 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 730 Project 15-31A ISSN 0077-5614 ISBN 978-0-309-25854-8 Library of Congress Control Number 2012947052 Â© 2012 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. On 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. Charles M. Vest 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, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg 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. Charles M. Vest 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 AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 15-31A. This report was prepared by Dr. Darren J. Torbic, Ms. Jessica M. Hutton, Ms. Courtney D. Bokenkroger, Mr. Douglas W. Harwood, Mr. David K. Gilmore, Ms. Melanie M. Knoshaug, and Mr. John J. Ronchetto of MRIGlobal (formerly Midwest Research Institute) and Mr. Marcus A. Brewer, Dr. Kay Fitzpatrick, Dr. Susan T. Chrysler, and Mr. Jesse Stanley of the Texas A&M Transportation Institute (TTI). The authors wish to thank the state departments of transportation of Kansas, Missouri, Pennsylvania, and Texas for their assistance in this research. CRP STAFF FOR NCHRP REPORT 730 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs B. Ray Derr, Senior Program Officer AndrÃ©a Harrell, Senior Program Assistant Eileen P. Delaney, Director of Publications Scott E. Hitchcock, Editor NCHRP PROJECT 15-31A PANEL Field of DesignâArea of General Design Larry F. Sutherland, Parsons Brinckerhoff, Columbus, OH (Chair) Kenneth T. Briggs, KCI Technologies Inc., Sparks, MD Silvia M. Fernandez, PB Americas, Inc., Miami, FL Amy Houser, Federal Emergency Management Agency, Washington, DC Rudolf Kolaja, Traffic Operations Engineering, LLC, Chandler, AZ John Roccanova, David Evans & Associates, Roseville, CA John L. Sanford, Mid-America Engineering Services, P.C., Springfield, IL Stephen F. Maher, TRB Liaison
F O R E W O R D ByâB.âRayâDerr StaffâOfficer TransportationâResearchâBoard This report presents design guidance for freeway mainline ramp terminals based on cur- rent driver and vehicle behavior. The report will be useful to freeway designers and those responsible for developing design standards for freeway ramps. Special attention was given to the behavior of tractor-trailers and the report includes several speed-distance curves for tractor-trailers on grades up to 9% that could be useful in other applications (e.g., climb- ing lanes). The design values for freeway ramps in the AASHTO Policy on Geometric Design of High- ways and Streets (Green Book) rely heavily on research conducted in the late 1930s and early 1940s, predating the development of the Interstate system. The studies relied entirely on passenger cars for acceleration and deceleration rates, without consideration of trucks and buses; this was based on the assumption that the acceleration distances for heavy vehicles would be âentirely out of reason.â Vehicle characteristics have changed since the original research. For example, the weight-to-horsepower ratio for trucks in 1965 was 400 lb/hp compared with the currently used ratio of 200 lb/hp. According to the Green Book, the mainline terminal of a ramp is that portion adjacent to the through traveled way, including speed-change lanes and tapers. There are two basic designs for freeway ramp terminals: tapered and parallel. Transportation agencies tend to adopt one of these designs as a standard (often different for entrances and exits), but there is little objective information available for designers on their relative strengths. In NCHRP Project 15-31, CH2M Hill, MRIGlobal, and the Texas Transportation Insti- tute reviewed the relevant literature and developed conceptual models for freeway entrance and exit maneuvers that represent the driverâs thought processes and decision points. Criti- cal factors and issues for ramp terminal design (including design vehicles) were described as well as interrelationships between them. The research team then prepared an updated work plan for collecting data, analyzing data, and developing design guidance for freeway mainline ramp terminals. Due to staffing changes, CH2M Hill withdrew from the research team and MRIGlobal and TTI continued the work in NCHRP Project 15-31A. Crash analysis was used to identify typical types of crashes at ramp terminals; observational field studies and driver behavioral studies were used to update basic assumptions in the equations. These results were then used to assess typical ramp terminal designs and develop design guidance for parallel and tapered freeway mainline ramp terminals. The following appendices are available on the TRB website (http://www.trb.org/Main/ Blurbs/167516.aspx):
â¢ Appendix A: Aerial View of Study Locations, â¢ Appendix B: Histograms of Observed Acceleration Rates, â¢ Appendix C: Verbal Instructions for Behavioral Study, and â¢ Appendix D: Potential Changes Proposed for Consideration in the Next Edition of the Green Book.
C O N T E N T S 1â Summary 6 Section 1â Introduction 6 1.1 Background 6 1.2 Objective and Scope 7 1.3 Overview of Research Methodology 7 1.4 Outline of Report 8 Section 2â LiteratureâReview 8 2.1 AASHTO Design Policies for Speed-Change Lanes and Freeway Mainline Ramp Terminals 11 2.2 Geometric Design and Safety 13 2.3 Vehicle Performance 13 2.4 Human Factors 14 2.5 Operational Issues at Freeway Mainline Ramp Terminals 15 2.6 Summary 16 Section 3â âAASHTOâModelsâforâFreewayâEntranceâ andâExitâTerminals 16 3.1 Freeway Mainline Entrance Terminals 17 3.2 Freeway Mainline Exit Terminals 19 3.3 Operational Assumptions of AASHTO Models 21 Section 4â âAnalysisâofâTruck-RelatedâCrashesâ NearâFreewayâMainlineâRampâTerminals 21 4.1 Overview of Crash Analysis 23 4.2 Analysis Results 29 4.3 Key Findings 33 Section 5â âObservationalâStudyâofâFreewayâ MainlineâRampâTerminals 33 5.1 Study Locations 37 5.2 Field Data Collection Procedures 40 5.3 Data Processing 43 5.4 Analysis Results 103 Section 6â âBehavioralâStudyâofâFreewayâ MainlineâRampâTerminals 103 6.1 Data Collection 105 6.2 Data Reduction 107 6.3 Entrance Ramp Analyses
110 6.4 Exit Ramp Analyses 114 6.5 Summary of Significant Findings 115 Section 7â ConclusionsâandâProposals 115 General Conclusions 115 Conclusions Specific to Entrance Ramps 116 Conclusions Specific to Exit Ramps 117 Potential Changes Proposed for Consideration in the Next Edition of the Green Book 118 Future Research Needs 119 Section 8â References 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.