National Academies Press: OpenBook

Selecting Ramp Design Speeds, Volume 1: Guide (2021)

Chapter: Front Matter

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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Selecting Ramp Design Speeds, Volume 1: Guide. Washington, DC: The National Academies Press. doi: 10.17226/26415.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Selecting Ramp Design Speeds, Volume 1: Guide. Washington, DC: The National Academies Press. doi: 10.17226/26415.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Selecting Ramp Design Speeds, Volume 1: Guide. Washington, DC: The National Academies Press. doi: 10.17226/26415.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Selecting Ramp Design Speeds, Volume 1: Guide. Washington, DC: The National Academies Press. doi: 10.17226/26415.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Selecting Ramp Design Speeds, Volume 1: Guide. Washington, DC: The National Academies Press. doi: 10.17226/26415.
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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2021. Selecting Ramp Design Speeds, Volume 1: Guide. Washington, DC: The National Academies Press. doi: 10.17226/26415.
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NCHRP Web-Only Document 313 Selecting Ramp Design Speeds VOLUME 1: GUIDE Darren J. Torbic MRIGlobal Kansas City, MO Marcus A. Brewer Michael P. Pratt Texas A&M Transportation Institute College Station, TX Final Guide for NCHRP Project 15-56 Submitted June 2021 NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed, and implementable research is the most effective way to solve many problems facing state departments of transportation (DOTs) administrators and engineers. Often, highway problems are of local or regional interest and can best be studied by state DOTs individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation results in increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. Recognizing this need, the leadership of the American Association of State Highway and Transportation Officials (AASHTO) in 1962 initiated an objective national highway research program using modern scientific techniques—the National Cooperative Highway Research Program (NCHRP). NCHRP is supported on a continuing basis by funds from participating member states of AASHTO and receives the full cooperation and support of the Federal Highway Administration (FHWA), United States Department of Transportation, under Agreement No. 693JJ31950003. 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, FTA, GHSA, NHTSA, or TDC 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. DISCLAIMER The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research. They are not necessarily those of the Transportation Research Board; the National Academies of Sciences, Engineering, and Medicine; the FHWA; or the program sponsors. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.

The National Academy of Sciences was established in 1863 by an Act of Congress, signed by President Lincoln, as a private, non- governmental institution to advise the nation on issues related to science and technology. Members are elected by their peers for outstanding contributions to research. Dr. Marcia McNutt is president. The National Academy of Engineering was established in 1964 under the charter of the National Academy of Sciences to bring the practices of engineering to advising the nation. Members are elected by their peers for extraordinary contributions to engineering. Dr. John L. Anderson is president. The National Academy of Medicine (formerly the Institute of Medicine) was established in 1970 under the charter of the National Academy of Sciences to advise the nation on medical and health issues. Members are elected by their peers for distinguished contributions to medicine and health. Dr. Victor J. Dzau is president. The three Academies work together as the National Academies of Sciences, Engineering, and Medicine to provide independent, objective analysis and advice to the nation and conduct other activities to solve complex problems and inform public policy decisions. The National Academies also encourage education and research, recognize outstanding contributions to knowledge, and increase public understanding in matters of science, engineering, and medicine. Learn more about the National Academies of Sciences, Engineering, and Medicine at www.nationalacademies.org. The Transportation Research Board is one of seven major programs of the National Academies of Sciences, Engineering, and Medicine. The mission of the Transportation Research Board is to provide leadership in transportation improvements and innovation through trusted, timely, impartial, and evidence-based information exchange, research, and advice regarding all modes of transportation. The Board’s varied activities annually engage about 8,000 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 individuals interested in the development of transportation. Learn more about the Transportation Research Board at www.TRB.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 WEB-ONLY DOCUMENT 313, Vol.1 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Camille Crichton-Sumners, Associate Program Manager, National Cooperative Highway Research Program Tyler Smith, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications Jennifer Correro, Assistant Editor NCHRP PROJECT 15-56 PANEL Field of Design—Area of General Design Luis Betancourt, California Department of Transportation (CALTRANS), Sacramento, CA (Chair) Leticia Sosa Estavillo, AIA Engineers, a CONSOR company, Austin, TX Theron Knouse, Virginia Department of Transportation, Richmond, VA Alejandra L. Medina, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, VA Hasmukh M. Patel, Massachusetts Department of Transportation, Boston, MA James Allen Rosenow, Minnesota Department of Transportation, Shoreview, MN Brian David Toombs, Burgess and Niple, Inc., Columbus, OH Mark A. Doctor, FHWA Liaison Stephen F. Maher, TRB Liaison ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 15-56, “Guidelines for Selecting Ramp Design Speeds.” This report was prepared by Dr. Darren J. Torbic (formerly with MRIGlobal), Mr. Marcus A. Brewer, and Mr. Michael P. Pratt of the Texas A&M Transportation Institute. Mr. Daniel J. Cook of HDR, Mr. Douglas W. Harwood of Harwood Road Safety LLC, and Ms. Heidi Ouren of HQE Incorporated played key roles in this research. The authors wish to thank the State Departments of Transportation of California, Kansas, Missouri, and Texas for their assistance in this research.

iv Table of Contents Summary ..........................................................................................................................................1 Section 1. Introduction ....................................................................................................................3 1.1 Background ...........................................................................................................3 1.2 Objective and Scope of Guidelines .......................................................................7 1.3 Concept and Definition of Ramp Design Speed ...................................................8 1.4 Related Terms and Definitions ............................................................................11 1.5 Outline of Document ...........................................................................................22 Section 2. Ramp Elements Related to Ramp Design Speed .........................................................23 2.1 System and Service Interchanges ........................................................................23 2.2 Ramp Configuration ............................................................................................25 2.3 Entrance and Exit Ramps ....................................................................................26 2.4 Freeway Mainline Ramp Terminal Configuration ..............................................29 2.5 Type of Crossroad Ramp Terminal .....................................................................29 2.6 Ramp Grade .........................................................................................................30 2.7 Type of Horizontal Curvature .............................................................................31 2.8 Number of Lanes .................................................................................................31 2.9 Crossover Crown Line ........................................................................................32 2.10 Superelevation and Superelevation Transition ....................................................33 2.11 Ramp Metering ....................................................................................................34 2.12 Collector-Distributor and Frontage Roads ..........................................................34 2.13 Physical Site Constraints, Environmental and Social Impacts, and Right-of- Way Costs ...........................................................................................................34 2.14 Ramp Design Speed Guide Values .....................................................................35 Section 3. Guidelines for Designing Ramps in a Consistent Manner Based on the Selected Ramp Design Speed .......................................................................................................................40 3.1 Design Guidelines ...............................................................................................40 3.2 Design Controls and Criteria for Ramps .............................................................41 3.3 Measures for Reducing Speeds on Exit Ramps ..................................................55 Section 4. Design Tool to Evaluate Ramp Designs for Consistency with the Selected Ramp Design Speed .................................................................................................................................57 4.1 Input Data for the RSPM .....................................................................................58 4.2 Output Data from the RSPM ...............................................................................66 4.3 RSPM Speed Calculations ..................................................................................72 4.4 Uses and Limitations of the RSPM .....................................................................89 Section 5. Case Studies .................................................................................................................92 5.1 Evaluating the Consistency of a Ramp Design for an Entrance Ramp at a Service Interchange Based on the Selected Ramp Design Speed .......................92 5.2 Evaluating the Consistency of a Ramp Design for an Exit Ramp at a Service Interchange Based on the Selected Ramp Design Speed ..................................109 Section 6. Summary of Design Guide and Future Research Needs ............................................122 Section 7. References ..................................................................................................................126

v Section 8. Abbreviations, Acronyms, Initialisms, and Symbols .................................................127 Figures Figure 1. Primary Components of a Ramp at a Service Interchange ............................................4 Figure 2. Primary Components of a Ramp at a System Interchange ............................................5 Figure 3. Illustration of Dividing the Ramp Proper of an Entrance Ramp into Individual Tangents and Curves ......................................................................................................9 Figure 4. Illustration of Dividing the Ramp Proper of an Exit Ramp into Individual Tangents and Curves ....................................................................................................10 Figure 5. Freeway Mainline Ramp Terminals (Entrance and Exit Ramps) ................................13 Figure 6. Diagonal Ramp ...........................................................................................................15 Figure 7. Loop and Semidirect Connection Ramps ....................................................................15 Figure 8. Direct Connection Ramp ..............................................................................................16 Figure 9. Outer Connection Ramp ..............................................................................................16 Figure 10. Taper-Type Entrance and Exit Ramps .........................................................................18 Figure 11. Parallel-Type Entrance and Exit Ramps ......................................................................18 Figure 12. Typical Exit Gore Area Characteristics .......................................................................19 Figure 13. Primary Components and Controlling Curves at Entrance and Exit Ramps at Service Interchanges ....................................................................................................38 Figure 14. Primary Components and Controlling Curve for Outer Connection Ramp at a System Interchange ......................................................................................................38 Figure 15. Acceleration of Passenger Cars, Level Condition .......................................................42 Figure 16. Primary Components of Freeway Mainline Ramp Terminal of an Entrance Ramp ....47 Figure 17. Freeway Mainline Ramp Terminal Elements of an Exit Ramp ...................................50 Figure 18. Deceleration Distances for Passenger Vehicles Approaching Intersections ................52 Figure 19. Elements of the Functional Area of a Crossroad Ramp Terminal ...............................53 Figure 20. Input Data for RSPM for Entrance Ramps ..................................................................60 Figure 21. Elements and Dimensions of Freeway Mainline Ramp Terminals Input into RSPM for Entrance Ramps ..........................................................................................61 Figure 22. Input Data for RSPM for Exit Ramps ..........................................................................64 Figure 23. Elements and Dimensions of Freeway Mainline Ramp Terminals Input into RSPM for Exit Ramps .................................................................................................65 Figure 24. Graphical Illustration of Vehicle Speeds for Sample Entrance Ramp .........................67 Figure 25. Graphical Illustration of Vehicle Speeds for Sample Exit Ramp ................................70 Figure 26. Revised Graphical Illustration of Vehicle Speeds for Sample Design Alternative (Exit Ramp) ..................................................................................................................72 Figure 27. Primary Components of an Entrance Ramp near the Freeway Mainline Ramp Terminal and Associated Speed Points of Interest ......................................................77 Figure 28. Graphical Illustration of Vehicle Speeds for Sample Entrance Ramp with Alternate Profile ...........................................................................................................82 Figure 29. Primary Components of an Exit Ramp near the Freeway Mainline Ramp Terminal and Associated Speed Points of Interest ......................................................83 Figure 30. Graphical Illustration of Vehicle Speeds for Sample Exit Ramp with Alternate Profile ...........................................................................................................................87 Figure 31. Case Study No. 1 (Entrance Ramp: General Ramp Characteristics and Dimensions) .................................................................................................................94

vi Figure 32. Case Study No. 1 (Entrance Ramp: Inputs to RSPM) .................................................97 Figure 33. Case Study No. 1 (Entrance Ramp: Outputs from RSPM) ..........................................98 Figure 34. Case Study No. 1 (Entrance Ramp: Revised Inputs to RSPM) .................................100 Figure 35. Case Study No. 1 (Entrance Ramp: Revised Outputs from RSPM) ..........................101 Figure 36. Case Study No. 2 (General Ramp Characteristics and Dimensions) .........................103 Figure 37. Case Study No. 2 (Entrance Ramp: Inputs to RSPM) ...............................................105 Figure 38. Case Study No. 2 (Entrance Ramp: Outputs from RSPM) ........................................106 Figure 39. Case Study No. 2 (Entrance Ramp: Revised Inputs to RSPM) .................................108 Figure 40. Case Study No. 2 (Entrance Ramp: Revised Outputs from RSPM) ..........................109 Figure 41. Case Study No. 3 (Exit Ramp: General Ramp Characteristics and Dimensions) ......111 Figure 42. Case Study No. 3 (Exit Ramp: Inputs to RSPM) .......................................................113 Figure 43. Case Study No. 3 (Exit Ramp: Outputs from RSPM) ...............................................114 Figure 44. Case Study No. 3 (Exit Ramp: Revised Outputs from RSPM)..................................116 Figure 45. Case Study No. 3 (Exit Ramp: General Ramp Characteristics and Dimensions) ......118 Figure 46. Case Study No. 4 (Exit Ramp: Inputs to RSPM) .......................................................120 Figure 47. Case Study No. 4 (Exit Ramp: Outputs from RSPM) ...............................................121 Tables Table 1. Guide Values for Ramp Design Speed as Related to Highway Design Speed ..............3 Table 2. Anticipated Driver Behavior and Ramp Design Speeds by System and Service Interchanges .................................................................................................................24 Table 3. Maximum Algebraic Difference in Cross Slope at Turning Roadway Terminals .......33 Table 4. Range of Guide Values for Ramp Design Speed as Related to Highway Design Speed, Interchange Type, Ramp Configuration, and Contextual Considerations .......37 Table 5. Minimum Lengths for Tangents and Curves on Ramp Proper of Entrance Ramps ....43 Table 6. Minimum Acceleration Lengths for Entrance Terminals with Flat Grades of Less Than 3 Percent .............................................................................................................45 Table 7. Minimum Deceleration Lengths for Exit Terminals with Flat Grades of Two Percent or Less .............................................................................................................49 Table 8. Deceleration Distances for Passenger Vehicles Approaching Intersections based on Steady Braking ........................................................................................................53 Table 9. Recommended Minimum Length to Queue at a Crosroad Ramp Terminal ................54 Table 10. Plotted Speed Data for Sample Entrance Ramp ..........................................................68 Table 11. Acceleration Rate Calculations for Sample Entrance Ramp .......................................69 Table 12. Plotted Speed Data for Sample Exit Ramp ..................................................................71 Table 13. Deceleration Rate Calculations for Sample Exit Ramp ...............................................71 Table 14. Entrance Ramp Acceleration Rates along Gap Acceptance Length, |Gr| < 2.5 percent ..........................................................................................................................78 Table 15. Entrance Ramp Acceleration Rates along Gap Acceptance Length, |Gr| ≥ 2.5 percent ..........................................................................................................................79 Table 16. Input Data for Ramp Curve Speed Prediction Procedures in ISATe ...........................80 Table 17. Exit Ramp Speed Differentials ....................................................................................83 Table 18. Case Study No. 1: Assessment of Design Speeds for Individiual Segment of the Ramp Proper and Minimum Acceleration Lengths .....................................................96

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Selection of a design speed should be based upon the anticipated operating speed, topography, adjacent land use, modal mix, and functional classification of the roadway.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 313: Selecting Ramp Design Speeds, Volume 1: Guide provides further detail for selecting an appropriate ramp design speed than presented in the 2018 Green Book, to address several overarching challenges that may lead to confusion or inconsistent interpretation of existing AASHTO guidance for selecting an appropriate ramp design speed.

Supplemental to the document are NCHRP Web-Only Document 313: Selecting Ramp Design Speeds,Volume 2: Conduct of Research Report and Ramp Speed Profile Model worksheets.

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