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ACKNOWLEDGMENT This work was sponsored by the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program (NCHRP), which is administered by the Transportation Research Board (TRB) of the National Academies. 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, Transit Development Corporation, or AOC 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 Research Council, 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 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 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. 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 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

i CONTENTS LIST OF FIGURES ..................................................................................................................... iv LIST OF TABLES ....................................................................................................................... vi AUTHOR ACKNOWLEDGMENTS......................................................................................... ix ABSTRACT ................................................................................................................................... x EXECUTIVE SUMMARY ......................................................................................................... xi CHAPTER 1 INTRODUCTION ................................................................................................. 1 BACKGROUND ........................................................................................................................ 1 OBJECTIVES ............................................................................................................................. 2 APPROACH ............................................................................................................................... 2 ORGANIZATION OF THIS REPORT ...................................................................................... 2 CHAPTER 2 LITERATURE REVIEW—INSTALLATION GUIDELINES ........................ 5 LEFT-TURN LANE INSTALLATION GUIDELINES ............................................................ 5 Guidelines Based on Risk ....................................................................................................... 5 Guidelines Based on Approaching Volumes ........................................................................ 12 Guidelines Developed Using Simulation Models ................................................................. 13 Guidelines Based on a Combination of Approaches ............................................................ 15 Summary of Guidelines from Literature ............................................................................... 17 Guidelines in State Manuals ................................................................................................. 17 RIGHT-TURN LANE INSTALLATION GUIDELINES ........................................................ 34 Guidelines Based on Volume................................................................................................ 34 Guidelines Based on Risk ..................................................................................................... 35 Guidelines Based on Benefit/Cost ........................................................................................ 36 Guidelines Based on a Combination of Approaches ............................................................ 42 CHAPTER 3 LITERATURE REVIEW—LEFT-TURN LANE DESIGN ........................... 43 AASHTO Green Book Material................................................................................................ 43 Deceleration Length .............................................................................................................. 43 Storage Length ...................................................................................................................... 44 Taper ..................................................................................................................................... 44 Width..................................................................................................................................... 45 Offset Left-Turn Lanes ......................................................................................................... 45 STATE MANUALS ................................................................................................................. 45 Queue Storage Length........................................................................................................... 46 Entering Taper Length .......................................................................................................... 47 Deceleration Length .............................................................................................................. 47 Width..................................................................................................................................... 47 Offset..................................................................................................................................... 47 Dual Turn Lanes ................................................................................................................... 48 TWLTL ................................................................................................................................. 49 Pedestrians ............................................................................................................................ 50 Indirect Turn Designs ........................................................................................................... 50

ii Bypass Lanes (or Blister Lanes) ........................................................................................... 50 PREVIOUS RESEARCH ......................................................................................................... 50 Left-Turn Lane Length ......................................................................................................... 51 Taper ..................................................................................................................................... 52 Left-Turn Lane Width ........................................................................................................... 53 Offset Left-Turn Lanes ......................................................................................................... 54 Intersection Sight Distance ................................................................................................... 58 Alternate Intersection Designs .............................................................................................. 59 SUMMARY OF LITERATURE .............................................................................................. 60 CHAPTER 4 DRIVER BEHAVIOR STUDY .......................................................................... 61 BACKGROUND ...................................................................................................................... 61 STUDY OBJECTIVES ............................................................................................................. 61 STUDY LOCATION ................................................................................................................ 61 DATA COLLECTION ............................................................................................................. 62 DATA REDUCTION ............................................................................................................... 62 RESULTS ................................................................................................................................. 64 Average Time-to-Clear or Time-to-Turn Values .................................................................. 64 Creating Prediction Equations .............................................................................................. 67 Critical Gap ........................................................................................................................... 73 CHAPTER 5 DELAY, CRASH, AND CONSTRUCTION COST STUDIES ....................... 81 ECONOMIC ANALYSIS PROCEDURE ................................................................................ 81 DELAY ..................................................................................................................................... 82 Scenarios ............................................................................................................................... 82 Simulation ............................................................................................................................. 83 Delay for Entire Year ............................................................................................................ 87 Travel Time Delay Savings .................................................................................................. 87 CRASHES................................................................................................................................. 88 Crash Prediction .................................................................................................................... 88 Accident Modification Factor ............................................................................................... 93 Comparison of Crash Prediction and Total Crashes at Selected Field Study Sites .............. 93 Volumes Used in Crash Prediction for Benefit-Cost Evaluations ........................................ 94 2009 Value of a Statistical Life by Crash Severity ............................................................... 94 Typical Crash Cost for Three-Leg and Four-Leg Intersections ............................................ 98 CONSTRUCTION COSTS .................................................................................................... 104 EXAMPLES OF CALCULATIONS FOR ADDING LEFT-TURN LANE AT EXISTING SITE ........................................................................................................................................ 106 Adding Left-Turn Lane at Existing Site on Rural Two-Lane Highway ............................. 106 Adding Left-Turn Lane on Existing Rural Four-Lane Highway ........................................ 108 Adding Left-Turn Lane to Existing Urban and Suburban Intersection .............................. 110 GREEN BOOK WARRANTS FOR LEFT-TURN LANE ..................................................... 112 DEVELOP PRELIMINARY WARRANTS FOR LEFT-TURN LANE ............................... 114 Plots of Preliminary Warrants ............................................................................................. 114 Observations Regarding Preliminary Warrants .................................................................. 121 Other Preliminary Warrants ................................................................................................ 121 IMPACTS DUE TO A NEW DEVELOPMENT ................................................................... 126

iii Example of New Development ........................................................................................... 128 CHAPTER 6 COMPARISON OF PROCEDURES .............................................................. 131 OVERVIEW OF IDENTIFIED PROCEDURES ................................................................... 131 CONFLICT AVOIDANCE (HARMELINK) PROCEDURE ................................................ 133 Limitations .......................................................................................................................... 133 Comparison between Harmelink Assumptions and Field Study Findings ......................... 134 Changes to Warrants ........................................................................................................... 136 BENEFIT-COST RATIO ....................................................................................................... 137 MINIMUM VOLUME/ENGINEERING JUDGMENT ......................................................... 142 LEFT-TURN LANE STORAGE ............................................................................................ 143 CHAPTER 7 SUMMARY AND CONCLUSIONS ................................................................ 151 SUMMARY ............................................................................................................................ 151 Objective ............................................................................................................................. 151 Literature Review................................................................................................................ 151 Legal Review ...................................................................................................................... 152 Interviews ............................................................................................................................ 152 Comparison of Existing Procedures.................................................................................... 153 Driver Behavior Study ........................................................................................................ 153 Updating Harmelink............................................................................................................ 154 Updating Harmelink Storage Lengths ................................................................................ 154 Economic Analysis for Existing Sites................................................................................. 154 Economic Analysis for New Sites ...................................................................................... 157 CONCLUSIONS..................................................................................................................... 157 APPENDIX A REVISED TEXT ON LEFT-TURN LANE WARRANTS FOR THE AASHTO GREEN BOOK ......................................................................................................... A-1 APPENDIX B REVISED TEXT ON LEFT-TURN LANE WARRANTS FOR THE TRB ACCESS MANAGEMENT MANUAL ............................................................................ B-1 APPENDIX C STATE WARRANTS/GUIDELINES FOR LEFT-TURN LANES ........... C-1 APPENDIX D INTERVIEW QUESTIONS ........................................................................... D-1 APPENDIX E INTERVIEWS ................................................................................................. E-1 APPENDIX F LEGAL REVIEW ............................................................................................. F-1 REFERENCES .......................................................................................................................... R-1

iv LIST OF FIGURES Figure 1. Volumes for use in left-turn lane warrant methods. ........................................................ 5 Figure 2. Harmelink (1) left-turn lane warrant graph for 40 mph and 5 percent left turns, 1967..................................................................................................................................... 6 Figure 3. NCHRP Report 279 (10) left-turn lane guidelines, 1985. ............................................... 8 Figure 4. Oppenlander and Bianchi (11) left-turn lane guidelines; unsignalized, two-lane, 30-mph operating speed, 1990. ........................................................................................... 9 Figure 5. Fitzpatrick and Wolff (13) comparison of existing to proposed guidelines (example uses 10 percent left turns), 2003. ...................................................................... 10 Figure 6. NCHRP Report 348 (15) left-turn lane guidelines, 1992. ............................................. 13 Figure 7. Hawley and Stover (17) left-turn lane guidelines for four-lane undivided arterial street with nonplatoon flow, 1996. ................................................................................... 14 Figure 8. Kikuchi and Chakroborty (19) left-turn lane guidelines using three methods, 1991................................................................................................................................... 16 Figure 9. Ranade et al. (18) and previous studies (1, 19) comparison of left-turn lane warrants (assuming 40-mph speed and 30 percent left turns), 2007................................. 17 Figure 10. Dual left-turn lane (63, 64). ......................................................................................... 53 Figure 11. Examples of offset left-turn lanes (63). ....................................................................... 55 Figure 12. Parallel and tapered offset left-turn lane (5). ............................................................... 57 Figure 13. Examples of equipment used for data collection. ........................................................ 64 Figure 14. Plot of average turning time by crossing distance. ...................................................... 66 Figure 15. Variable’s contribution to predicting turning time using low, middle, and high values. ............................................................................................................................... 70 Figure 16. Variables’ contribution to predicting turning time by crossing width. ....................... 71 Figure 17. Turning time by posted speed limit (assumed two-lane highway). ............................. 72 Figure 18. Plot of logit model for three field sites. ....................................................................... 76 Figure 19. Illustration of Raff/Hart graphical method for identifying critical gap. ...................... 76 Figure 20. Plot of median gap acceptance for 25-mph and 55-mph sites from this field study and Yan et al. (76). .................................................................................................. 79 Figure 21. Gap acceptance result by crossing distance for field study sites. ................................ 79 Figure 22. Gap acceptance result by crossing distance group for field study sites. ..................... 80 Figure 23. Simulation-estimated delay reduction when adding a left-turn lane at an existing site. ...................................................................................................................... 84 Figure 24. Simulation-estimated added delay for a new development (no left-turn lane scenario). ........................................................................................................................... 85 Figure 25. Illustration of predicted crash frequency using Highway Safety Manual equations. .......................................................................................................................... 93 Figure 26. Comparison between actual crashes and predicted crashes for a sample of field study sites. ......................................................................................................................... 94 Figure 27. Plot of Green Book rural two-lane highway left-turn warrant values. ...................... 113 Figure 28. Lines generated to represent a subset of the Green Book rural two-lane highway left-turn warrant values. ................................................................................... 113 Figure 29. Range of left-turn lane warrants based on crash costs (low, mid-, and high range) for rural two-lane highway. ................................................................................. 115

v Figure 30. Range of left-turn lane warrants based on crash costs (low, mid-, and high range) for rural four-lane highway. ................................................................................. 116 Figure 31. Range of left-turn lane warrants based on crash costs (low, mid-, and high range) for urban and suburban highways. ....................................................................... 117 Figure 32. Range of left-turn lane warrants based on construction costs (minimum, moderate, and maximum) for rural two-lane highways. ................................................. 118 Figure 33. Range of left-turn lane warrants based on construction costs (minimum, moderate, and maximum) for rural four-lane highways. ................................................ 119 Figure 34. Range of left-turn lane warrants based on construction costs (minimum, moderate, and maximum) for urban and suburban arterials. .......................................... 120 Figure 35. Suggested left-turn warrants based on results from benefit-cost evaluation when using B/C of 1.0 and mid-range crash cost and moderate construction cost. ....... 122 Figure 36. Suggested left-turn warrants based on results from benefit-cost evaluation when using B/C of 2.0 and mid-range crash cost and moderate construction cost. ....... 123 Figure 37. Suggested left-turn warrants based on results from benefit-cost evaluation when using B/C of 1.0 and HSM crash costs (2009 dollars). ......................................... 126 Figure 38. Example of change in Green Book (GB) left-turn lane warrants if findings from field study (Field) are used in the Harmelink procedure for a 60-mph two- lane highway. .................................................................................................................. 137 Figure 39. Suggested left-turn lane warrants based on results from benefit-cost evaluations for intersections on urban and suburban arterials. ....................................... 138 Figure 40. Suggested left-turn treatment warrants based on results from benefit-cost evaluations for intersections on rural two-lane highways............................................... 139 Figure 41. Suggested left-turn lane warrants based on results from benefit-cost evaluations for intersections on rural four-lane highways. ............................................. 140 Figure 42. Comparison of suggested left-turn lane warrants for rural two-lane highways. ....... 141 Figure 43. Comparison of suggested bypass lane warrants for rural two-lane highways........... 142 Figure 44. Storage length recommendations based on work by Harmelink (1). ........................ 146 Figure 45. Storage length recommendations based on work by Leisch (93) as presented in the TRB Access Management Manual (91). ................................................................... 147 Figure 46. Recommended storage lengths for left-turn lanes at uncontrolled approaches using a 25-ft minimum storage length along with a critical gap of 4.1 sec (12). ........... 149 Figure A-1. Suggested left-turn lane warrants based on results from benefit-cost evaluations for intersections on urban and suburban arterials. ....................................... A-4 Figure A-2. Suggested left-turn treatment warrants based on results from benefit-cost evaluations for intersections on rural two-lane highways............................................... A-5 Figure A-3. Suggested left-turn lane warrants based on results from benefit-cost evaluations for intersections on rural four-lane highways. ............................................. A-6 Figure B-1. Suggested left-turn lane warrants based on results from benefit-cost evaluations for intersections on urban and suburban arterials. ....................................... B-2 Figure B-2. Suggested left-turn treatment warrants based on results from benefit-cost evaluations for intersections on rural two-lane highways............................................... B-3 Figure B-3. Suggested left-turn lane warrants based on results from benefit-cost evaluations for intersections on rural four-lane highways. ............................................. B-4

vi LIST OF TABLES Table 1. Expected percent reduction for adding turn lane identified in FHWA study (2). ............ 2 Table 2. AASHTO (5) guide for left-turn lanes on two-lane highways, 2004. .............................. 7 Table 3. Fitzpatrick and Wolff (13) guidelines for installing left-turn lanes on two-lane highways, 2003. ................................................................................................................ 11 Table 4. Van Schalkwyk and Stover (14) recommended left-turn warrants on two-lane highways to accommodate the needs of older drivers, 2007. ........................................... 12 Table 5. Modur et al. (16) left-turn lane warrant chart, 1990. ...................................................... 14 Table 6. Summary of selected left-turn lane literature guidelines based on Harmelink procedure........................................................................................................................... 18 Table 7. Summary of selected left-turn lane literature guidelines based on approaching volume, delay, or combination of approaches. ................................................................. 18 Table 8. Summary of state methods. ............................................................................................. 19 Table 9. Colorado Access Code (38) criteria for deceleration lanes. ........................................... 23 Table 10. Georgia (45) regulations for driveway and encroachment control left-turn requirements, condition 1.................................................................................................. 25 Table 11. Georgia (45) regulations for driveway and encroachment control left-turn requirements, condition 2.................................................................................................. 25 Table 12. New Mexico (46) criteria for deceleration lanes on urban two-lane highways. ........... 26 Table 13. New Mexico (46) criteria for deceleration lanes on urban multilane highways. .......... 27 Table 14. New Mexico (46) criteria for deceleration lanes on rural two-lane highways. ............ 28 Table 15. New Mexico (46) criteria for deceleration lanes on rural multilane highways. ........... 28 Table 16. Iowa (47), left-turn lane material. ................................................................................. 29 Table 17. South Dakota (50) introduction material and criterion 1. ............................................. 30 Table 18. South Dakota (50) criterion 2 and 3 and evaluation guidelines. ................................... 31 Table 19. Minnesota (48) left-turn material. ................................................................................. 32 Table 20. Minnesota Mn/DOTAccess Management Manual (52) warrant for left-turn lanes. ................................................................................................................................. 33 Table 21. Nevada (23) left-turn lane requirements for multilane roads (unsignalized). ............... 33 Table 22. Nevada (23) left-turn lane requirements for multilane divided roads (unsignalized). ................................................................................................................... 33 Table 23. Summary of state design practice in providing right-turn lanes on rural highways (10).................................................................................................................... 35 Table 24. Potts et al. (58) equation used to determine benefit/cost ratio. ..................................... 37 Table 25. Potts et al. (58) delay reduction provided by provision of a right-turn lane on a two-lane arterial (sec/through veh). .................................................................................. 38 Table 26. Potts et al. (58) delay reduction provided by provision of a right-turn lane on a four-lane arterial (sec/through veh). ................................................................................. 39 Table 27. Potts et al. (58) additional delay reduction provided by right-turn lane where pedestrian activity is present (sec/through veh). ............................................................... 40 Table 28. Potts et al. (58) example of how annual delay reduction benefit was calculated. ........ 40 Table 29. Potts et al. (58) equations for predicting accident frequency. ...................................... 41 Table 30. Potts et al. (58) accident modification factors for right-turn lanes. .............................. 41 Table 31. Accident cost and severity distributions (58). .............................................................. 42 Table 32. Hai and Thakkar (59) critical right-turn volumes for different operating speeds. ........ 42

vii Table 33. Summary of left-turn lane design guidelines. ............................................................... 46 Table 34. Gard (61) regression equations for major-street left-turn queue length at unsignalized intersections. ................................................................................................ 51 Table 35. Tarawneh and McCoy (66) guidelines for offsetting opposing left-turn lanes............. 56 Table 36. Yan and Radwan (68) calculated available sight distance for traditional parallel opposing left-turn lanes..................................................................................................... 58 Table 37. Summary of left-turn lane design guidelines from the literature. ................................. 60 Table 38. Site characteristics. ....................................................................................................... 63 Table 39. Time-to-clear and time-to-turn values for passenger cars starting from a stopped position at each site. ............................................................................................ 65 Table 40. Comparisons of turning times for passenger cars. ........................................................ 67 Table 41. Regression model for turning time. .............................................................................. 69 Table 42. Logistic regression coefficients for field sites. ............................................................. 75 Table 43. Results for gap acceptance methods. ............................................................................ 77 Table 44. Mean values of gap (sec). ............................................................................................. 78 Table 45. Regression coefficients to predict the delay determined from simulation.................... 86 Table 46. Predicted delays. ........................................................................................................... 86 Table 47. Factors used to convert sec/veh delay to hr/intersection delay for a year. ................... 88 Table 48. National congestion constants used in the 2009 Urban Mobility Report (78). a ........... 88 Table 49. Safety performance functions for rural highways for total crashes. ............................. 89 Table 50. Safety performance functions for urban and suburban arterials for total crashes. ....... 90 Table 51. Definitions for variables in Table 50. ........................................................................... 91 Table 52. Minimum and maximum AADT for Highway Safety Manual equations. .................... 92 Table 53. Human capital cost and comprehensive societal cost from the Highway Safety Manual with factors for subsequent analyses.a ................................................................. 95 Table 54. Low, mid-range, and high comprehensive societal cost estimates (2008 dollars). ............................................................................................................................. 96 Table 55. Low, mid-range, and high human capital cost estimates (2008 dollars). ..................... 96 Table 56. Cost difference between comprehensive societal cost estimates and human capital cost estimates (2008 dollars). ................................................................................ 97 Table 57. 2009 CPI-adjusted human capital cost estimates (2009 dollars). ................................. 97 Table 58. 2009 ECI-adjusted cost difference between comprehensive societal cost estimates and human capital cost estimates (2009 dollars). ............................................. 98 Table 59. 2009 Comprehensive societal cost estimates (2009 dollars). ....................................... 98 Table 60. Default distribution of crash severity level at rural two-lane two-way intersections from the Highway Safety Manual (77). ....................................................... 99 Table 61. Injuries per crash for red-light-running crashes (83). ................................................... 99 Table 62. Injuries or deaths per crash for rural intersections.a ................................................... 100 Table 63. Typical crash cost calculations for three-leg rural intersections. ................................ 101 Table 64. Typical crash cost calculations for four-leg intersections. ......................................... 102 Table 65. Typical crash cost calculations for urban and suburban intersections. ....................... 103 Table 66. Crash cost estimates by crash severity from the Highway Safety Manual (77). ......... 103 Table 67. Typical crash cost by number of legs and rural or urban based on Highway Safety Manual crash costs. .............................................................................................. 104 Table 68. Estimated construction cost from literature. ............................................................... 105 Table 69. Construction cost for left-turn lane projects from four states. .................................... 105

viii Table 70. Calculation of annual delay savings for rural two-lane highway example. ................ 107 Table 71. Calculation of annual delay savings for rural four-lane highway example. ............... 109 Table 72. Calculation of annual delay savings for urban and suburban example....................... 110 Table 73. Range of left-turn lane warrants based on results from benefit-cost evaluations using crash costs developed based on FHWA economic value of a statistical life. ....... 124 Table 74. Range of left-turn lane warrants based on results from benefit-cost evaluations using crash costs developed from Highway Safety Manual crash costs. ........................ 125 Table 75. Calculation of annual delay for new development example. ...................................... 129 Table 76. Characteristics of procedures evaluated. .................................................................... 132 Table 77. Characteristics of other procedures identified during the course of this study. .......... 133 Table 78. Values for critical gap. ................................................................................................ 134 Table 79. Values for time to clear. .............................................................................................. 135 Table 80. Suggested left-turn lane warrants based on results from benefit-cost evaluations for urban and suburban arterials. .................................................................................... 138 Table 81. Suggested left-turn treatment warrants based on results from benefit-cost evaluations for rural two-lane highways. ........................................................................ 139 Table 82. Suggested left-turn lane warrants based on results from benefit-cost evaluations for rural four-lane highways. .......................................................................................... 140 Table 83. Queue storage length per vehicle (91). ....................................................................... 143 Table 84. Equations used to determine storage length. .............................................................. 144 Table 85. Recommended storage lengths from Access Management Manual equation and NCHRP Report 457 equations with revised critical gap. ................................................ 145 Table A-1. Suggested left-turn lane warrants based on results from benefit-cost evaluations for urban and suburban arterials. ................................................................. A-4 Table A-2. Suggested left-turn treatment warrants based on results from benefit-cost evaluations for rural two-lane highways. ........................................................................ A-5 Table A-3. Suggested left-turn lane warrants based on results from benefit-cost evaluations for rural four-lane highways. ....................................................................... A-6 Table B-1. Suggested left-turn lane warrants based on results from benefit-cost evaluations for urban and suburban arterials. ................................................................. B-2 Table B-2. Suggested left-turn treatment warrants based on results from benefit-cost evaluations for rural two-lane highways. ........................................................................ B-3 Table B-3. Suggested left-turn lane warrants based on results from benefit-cost evaluations for rural four-lane highways. ....................................................................... B-4 Table B-4. Recommended Storage Lengths for Arterials from Access Management Manual Equation and NCHRP Report 457 Equations with Revised Critical Gap. ........ B-9 Table B-5. Equations Used to Determine Storage Length. ....................................................... B-10

ix AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under National Cooperative Highway Research Program (NCHRP) Project 3-91 by the Texas Transportation Institute (TTI), Texas A&M University, Jerome S. Gluck of AECOM, and Herbert S. Levinson. The Texas A&M Research Foundation was the contractor for this study. Kay Fitzpatrick, TTI senior research engineer, was the principal investigator. The other authors of this report are Marcus A. Brewer (assistant research engineer, TTI), Jerome S. Gluck (associate vice president, AECOM), William L. Eisele (research engineer, TTI), Yunlong Zhang (assistant professor, Texas A&M University; assistant research scientist, TTI), Herbert S. Levinson (principal, Herbert S. Levinson, Transportation Consultant), Wyndylyn von Zharen (professor, Texas A&M University at Galveston), Matthew R. Lorenz (senior traffic engineer, AECOM), Vichika Iragavarapu (assistant transportation researcher, TTI), and Eun Sug Park (associate research scientist, TTI). The work was performed under the general supervision of Dr. Fitzpatrick. The authors wish to acknowledge the many individuals who contributed to this research by participating in the phone interviews (whose names cannot be reported here), assisting with field study site selection, and helping with field data collection and reduction. Those individuals include (but are not limited to): • Richard Calvache, field supervisor, AECOM; • Robert Medland, vice president/senior project manager, 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, 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, Fellow, 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, Arizona; • Kerry Wilcoxon, City of Phoenix, Arizona; • Troy Rother, City of College Station, Texas; • LuAnn Roth, Kansas Department of Transportation; • Lloyd Smith, Harris County, Texas; and • Narciso Lira III, City of Pearland, Texas.

x ABSTRACT Left-turn movements at intersections, including driveways—especially movements that are made from lanes that are shared with through traffic—cause delays and adversely impact safety. Although left-turn warrants have been updated, many agencies still use research performed by M. Harmelink from the mid-1960s. While most states use procedures that are based on Harmelink, a number of limitations of Harmelink’s procedure have been identified. Economic analysis can provide a useful method for combining traffic operations and safety benefits of left- turn lanes to identify situations in which left-turn lanes are and are not justified economically. This project used a benefit-cost approach to determine when a left-turn lane would be justified. The steps included simulation to determine delay savings from installing a left-turn lane, crash costs and crash reduction savings determined from safety performance functions and accident modification factors available in the Highway Safety Manual, and construction costs. Left-turn lane warrants were developed for rural two-lane highways, rural four-lane highways, and urban and suburban roadways. In addition, warrants for bypass lanes were developed for rural two-lane highways. A Design Guide on Left-Turn Accommodations at Unsignalized Intersections was developed that discusses left-turn lane designs, traffic control treatments, and case study examples.

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Development of Left-Turn Lane Warrants for Unsignalized Intersections Get This Book
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TRB’s National Cooperative Highway Research Program (NCHRP) Web-Only Document 193: Development of Left-Turn Lane Warrants for Unsignalized Intersections provides background on the development of NCHRP Report 745: Left-Turn Accommodations at Unsignalized Intersections.

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