Left-Turn Accommodations at Unsignalized Intersections (2013)

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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 745 Left-Turn Accommodations at Unsignalized Intersections Kay Fitzpatrick Marcus A. Brewer William L. Eisele Texas a&M TransporTaTion insTiTuTe College Station, TX Herbert S. Levinson Wallingford, CT Jerome S. Gluck Matthew R. Lorenz aeCoM New York, NY Subscriber Categories Highways  •  Design  •  Safety and Human Factors TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2013 www.TRB.org  Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

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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 745 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs B. Ray Derr, Senior Program Officer Andréa Harrell, Senior Program Assistant Eileen P. Delaney, Director of Publications Margaret B. Hagood, Editor NCHRP PROJECT 03-91 PANEL Field of Traffic—Area of Operations and Control Brian K. Gage, Minnesota DOT, St. Paul, MN (Chair) Gary Sokolow, Florida DOT, Tallahassee, FL Michael J. Fuess, Nevada DOT, Sparks, NV Chris W. Huffman, Kansas and Missouri Certified General Property Appraiser, Lawrence, KS Robert L. Irish, Kentucky Transportation Cabinet, Frankfort, KY Alejandra L. Medina-Flintsch, Virginia Tech Transportation Institute, Blacksburg, VA Vergil G. Stover, Texas A&M University, College Station, TX Wei Zhang, FHWA Liaison Richard A. Cunard, TRB Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 3-91 by the Texas Transportation Institute (TTI), Texas A&M University. Texas A&M Research Foundation was the contractor for this study. Kay Fitzpatrick, Senior Research Engineer, TTI, was the Principal Investigator. The other authors of this report are: Marcus A. Brewer (Assistant Research Engineer, TTI), Herbert S. Levinson (Principal, Herbert S. Levinson, Transportation Consultant), Jerome Gluck (Associate Vice President, AECOM), Matthew R. Lorenz (Senior Traffic Engineer, AECOM), and William L. Eisele (Research Engineer, TTI). The work was performed under the general supervision of Dr. Fitzpatrick. The authors wish to acknowledge those who contributed to this research, including (but are not limited to): Yunlong Zhang, Assistant Professor, Texas A&M University and Assistant Research Scientist, TTI; Wyndylyn von Zharen, Professor, Texas A&M University at Galveston; Vichika Iragavarapu, Assistant Transportation Researcher, TTI; Eun Sug Park, Associate Research Scientist, TTI; Richard Calvache, Field Supervisor, AECOM; Robert Medland, Vice-President, Traffic Research and Analysis, Inc.; Lisa Walters, Administrative Assistant, Traffic Research and Analysis, Inc.; Joseph Kaluha, Senior Manual Count Field Supervisor, Traffic Research and Analysis, Inc.; Will Fox, ATR Field Technician II, Traffic Research and Analysis, Inc.; Marcia Halilton, Manual Count Field Supervisor, Traffic Research and Analysis, Inc.; Anthony Voigt, Program Manager, TTI; Byung-Jung Park, Graduate Student, Texas A&M University; Colleen Dau, Lead Office Assistant, TTI; Christopher Senesi, Texas A&M University, Undergraduate Fellows Program; Dan Walker, Assistant Research Specialist, TTI; Feng Wan, Graduate Student, Texas A&M University; James Campbell, Student Worker, TTI; James Robertson, Graduate Student, Texas A&M University; Jesse Stanley, Research Associate, TTI; Jordan Main, Student Worker, TTI; Rickilee Mercer, Student Worker, TTI; Mike Cynecki, City of Phoenix, AZ; Kerry Wilcoxon, City of Phoenix, AZ; Troy Rother, City of College Station, TX; LuAnn Roth, Kansas DOT; Lloyd Smith, Harris County, TX; and Narciso Lira III, City of Pearland, TX.

F O R E W O R D By B. Ray Derr Staff Officer Transportation Research Board This report presents guidance for the selection and design of left-turn accommodations at unsignalized intersections. Eleven case studies of typical situations illustrate the use of the guidance. The report will be useful to geometric designers and traffic engineers that deal with unsignalized intersections. Maximizing the potential capacity of existing roadways is a priority in light of grow- ing traffic demands and the diminishing resources to develop more capacity. Left turns at unsignalized intersections, including driveways, cause delay and may reduce safety. The decision to install a left-turn accommodation is a complex one as state and local trans- portation agencies weigh the left-turn demand, the cost of the accommodation, and the anticipated operational and safety benefits. Clear and consistent application of left-turn accommodations is important for mitigating the impacts of left turns, both for reconstruc- tion projects and for the permitting of new access points. In NCHRP Project 03-91, the Texas A&M Transportation Institute and their research team interviewed state and local elected officials and transportation agency administrators, business owners, and developers to determine their concerns related to providing left-turn accommodations at unsignalized intersections and identify performance measures that may influence these decisions. They then developed a process for determining whether a left-turn accommodation is justified at an unsignalized intersection and, if so, the types of accommodations that are appropriate. The process considers safety, operational efficiency, and construction costs. Design guidance was then developed for typical left-turn accom- modations. The likely benefits and impacts of accommodations are described. This report includes eleven design examples illustrating use of the guidance. These exam- ples are based on actual locations where left-turn treatments were considered, evaluated, and/or installed. Two of the examples involve analysis of a proposed development. The contractor’s final report providing background information for the project is avail- able on the TRB website. In addition to describing the work that was done, Appendix F presents a legal review of the impact of essential nexus and rough proportionality on devel- opment considerations.

C O N T E N T S 1  Summary 3 Chapter 1  Introduction 3 Background of Study 4 Purpose and Scope of Guidelines 4 Organization of Design Guide 5 Chapter 2  Planning and Design Process 5 Introduction 5 Assemble Basic Information 5 Basic Information 6 Volume 6 Speed 6 Crash History 6 Delay 7 Establish and Apply Decision Criteria 8 Apply Left-Turn Lane Warrants 8 Warrants 8 Source of Warrants—Benefit-Cost Approach 11 Prepare Designs 12 Chapter 3  Geometric Design 12 Introduction 12 Selection of Design Speed 12 Selection of Design Vehicle 13 Desirable and Minimum Lane Widths 13 Tapers 14 Tapers for Left Turns (Bay Taper) 15 Tapers for Through Traffic (Approach Taper) 16 Deceleration Length 17 Vehicle Storage Length 19 Sight Distance 19 Median Design 20 Channelization and Offset 20 Bypass Lanes 22 Pedestrian Storage 23 Chapter 4  Traffic Controls and Illumination 23 Introduction 23 Signs 23 Sign Types 23 Sign Design

24 Placement 25 Application Guidelines 26 Pavement Markings 26 Overview 26 Types of Markings 26 Applications 27 Illumination 27 Overview 27 Types of Illumination 28 Intensity 28 Location 29 Provision for Future Signalization 29 Power 29 Location of Signal Poles and Controller Cabinet 29 Vehicle Detection 29 Access Management 30 Chapter 5  Design Examples 30 Introduction 30 Design Application #1: Installation of Exclusive Left-Turn Lanes at an Unsignalized Intersection in a Suburban Fringe Area 30 Context 31 Design Considerations and Analysis 32 Design Result 32 Design Application #2: Installation of an Exclusive Left-Turn Lane at an Unsignalized Intersection Between a Local Street and a State Highway 32 Context 32 Design Request 34 Design Considerations and Analysis 34 Design Result 34 Design Application #3: Addition of a Left-Turn Lane as Part of a “Road Diet” Treatment (Conversion of a Four-Lane Cross Section to a Three-Lane Cross Section) 34 Context 34 Design Request 34 Design Considerations and Analysis 35 Design Result 35 Design Application #4: Installation of Left-Turn Lanes at an Unsignalized Rural Intersection Between a State Highway and a Local Road 36 Context 36 Design Request 36 Design Considerations and Analysis 37 Design Result 37 Design Application #5: Installation of Unsignalized “J-Turn” Intersections Along a State Highway 37 Context 38 Design Request 38 Design Considerations and Analysis 39 Design Result

39 Design Application #6: Installation of a Left-Turn Passing Blister at an Unsignalized Intersection Between a Local Street and a State Highway 40 Context 40 Design Request 40 Design Considerations and Analysis 40 Design Result 41 Design Application #7: Installation of Left-Turn Lanes at an Unsignalized Rural Intersection Between a State Highway and a County Road 41 Context 42 Design Request 42 Design Considerations and Analysis 43 Design Result 43 Design Application #8: Follow-Up Traffic Studies to Verify the Need for an Unsignalized Left-Turn Lane in Conjunction with a Proposed Development 43 Context 43 Design Request 43 Design Considerations and Analysis 44 Design Result 45 Design Application #9: Installation of Left-Turn Lanes at Unsignalized Intersections in Conjunction with a Proposed Development 45 Context 45 Design Request 45 Design Considerations and Analysis 46 Design Result 46 Design Application #10: Installation of an Exclusive Left-Turn Lane at an Unsignalized Suburban Intersection Between a State Highway and a Local Street 46 Context 47 Design Request 47 Design Considerations and Analysis 48 Design Result 48 Design Example #11: Installation of Exclusive Left-Turn Lanes and a Traffic Signal at an Unsignalized Intersection Between a Local Street and a State Highway 49 Context 49 Design Request 49 Design Considerations and Analysis 50 Design Result 51  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.