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Highway Safety Manual User Guide (2022)

Chapter:Front Matter

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Suggested Citation:"Front Matter." National Academies of Sciences, Engineering, and Medicine. 2022. Highway Safety Manual User Guide. Washington, DC: The National Academies Press. doi: 10.17226/26552.
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NCHRP Web-Only Document 323 Highway Safety Manual User Guide K. Kolody D. Perez-Bravo J. Zhao T. R. Neuman CH2M HILL Chicago, IL Conduct of Research Report for NCHRP Project 17-50 Submitted August 2014 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 323 Christopher J. Hedges, Director, Cooperative Research Programs Lori L. Sundstrom, Deputy Director, Cooperative Research Programs Waseem Dekelbab, Associate Program Manager, National Cooperative Highway Research Program David Jared, Senior Program Officer Clara Schmetter, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications Jennifer Correro, Assistant Editor NCHRP PROJECT 17-50 PANEL Field of Traffic—Area of Safety Priscilla Tobias, Arora and Associates, P.C., Springfield, IL (Chair) Timothy Barnett, University of Alabama, Troy, AL Darryl Belz, Maine Department of Transportation, Augusta, ME Craig Copelan, American Society of Civil Engineers, Winters, CA Scott Jones, Utah Department of Transportation, Salt Lake City, UT Dean Kanitz, Michigan Department of Transportation, Lansing, MI Daniel Magri, Louisiana Department of Transportation and Development, Baton Rouge, LA Michelle Marshall, New Hampshire DOT, Concord, NH John Milton, Washington State Department of Transportation, Olympia, WA Jonathan Nelson, Missouri Department of Transportation, Jefferson City, MO Stephen Read, Virginia Department of Transportation, Richmond, VA Joseph Santos, Florida Department of Transportation, Tallahassee, FL Derek Troyer, Federal Highway Administration (FHWA), Columbus, OH Jerry Roche, FHWA Liaison Kelly Hardy, AASHTO Liaison Bernardo B. Kleiner, TRB Liaison ACKNOWLEDGMENT This report was performed under NCHRP Project 17-50, Lead State Initiative for Implementing the Highway Safety Manual by CH2M HILL, along with the HSM Lead States. These states are Alabama, California, Florida, Illinois, Louisiana, Maine, Michigan, Missouri, New Hampshire, Ohio, Utah, Virginia, and Washington. The project is managed by Mark Bush, NCHRP Senior Program Officer.

iv Contents SECTION PAGE 1 Introduction ............................................................................................................................ 1 1.1 Background ................................................................................................................................. 1 1.2 Using the Highway Safety Manual User Guide ........................................................................... 1 2 Highway Safety Manual Overview ........................................................................................... 3 2.1 HSM Part A: Introduction, Human Factors, and Fundamentals ................................................. 3 2.2 HSM Part B: Roadway Safety Management Process .................................................................. 4 2.2.1 HSM Chapter 4: Network Screening ...................................................................... 5 2.2.2 HSM Chapter 5: Diagnosis ..................................................................................... 6 2.2.3 HSM Chapter 6: Select Countermeasures ............................................................. 7 2.2.4 HSM Chapter 7: Economic Appraisal ..................................................................... 8 2.2.5 HSM Chapter 8: Prioritize Projects ........................................................................ 8 2.2.6 HSM Chapter 9: Safety Effectiveness Evaluation ................................................... 9 2.3 HSM Part C: Predictive Method ................................................................................................ 10 2.3.1 Overview of the Predictive Method .................................................................... 10 2.3.2 HSM Part C Relationship to HSM Parts A, B, and D ............................................. 12 2.3.3 Predicted versus Expected Crash Frequency ....................................................... 12 2.3.4 Safety Performance Functions ............................................................................. 13 2.3.5 Crash Modification Factors .................................................................................. 15 2.3.6 Weighting Using the Empirical Bayes Method .................................................... 15 2.3.7 Calibration versus Development of Local SPFs .................................................... 16 2.3.8 Crash Severity and Collision Type Distribution for Local Conditions ................... 16 2.3.9 Methods for Estimating the Safety Effectiveness of a Proposed Project ............ 16 2.3.10 Limitations of the HSM Predictive Method ......................................................... 17 2.3.11 HSM Part C Summary ........................................................................................... 18 2.3.12 HSM Chapter 10: Predictive Method for Rural Two-Lane, Two-Way Roads ....... 19 2.3.13 Calculating the Crash Frequency for Rural Two-Lane, Two-Way Roads .............. 21 2.3.14 Data Requirements for Rural Two-Lane, Two-Way Roads .................................. 25 2.3.15 HSM Chapter 11: Predictive Method for Rural Multilane Highways ................... 27 2.3.16 Calculating the Crash Frequency for Rural Multilane Highways .......................... 29 2.3.17 Data Requirements for Rural Multilane Highways .............................................. 34 2.3.18 HSM Chapter 12: Predictive Method for Urban and Suburban Arterials ............ 36 2.3.19 Calculating the Crash Frequency for Urban and Suburban Arterials ................... 38 2.3.20 Data Requirements for Urban and Suburban Arterials ....................................... 44 2.4 HSM Part D: CMF Applications Guidance ................................................................................. 47 2.4.1 HSM Chapter 13: Roadway Segments ................................................................. 48 2.4.2 HSM Chapter 14: Intersections ............................................................................ 49 2.4.3 HSM Chapter 15: Interchanges ............................................................................ 49 2.4.4 HSM Chapter 16: Special Facilities and Geometric Situations ............................. 50 2.4.5 HSM Chapter 17: Road Networks ........................................................................ 50 3 Integrating the HSM in the Project Development Process ...................................................... 52 3.1 HSM in the Planning Phase ....................................................................................................... 53 3.1.1 Overview .............................................................................................................. 53 3.1.2 Example Problem 1: Planning Application using HSM Part B .............................. 53

CONTENTS v 3.2 HSM in the Alternatives Development and Analysis Phase ...................................................... 61 3.2.1 Overview .............................................................................................................. 61 3.2.2 Example Problem 2: Rural, Two-Lane, Two-Way Roads and Rural Multilane Highway ............................................................................................................... 61 3.2.3 Part 1 – Rural Two-Lane Two-Way Roads ............................................................ 63 3.2.4 Part 2 – Rural Multilane Highways ....................................................................... 76 3.2.5 Example Problem 3: Urban and Suburban Arterials ............................................ 86 3.3 HSM in Design ......................................................................................................................... 108 3.3.1 Overview ............................................................................................................ 108 3.3.2 Example Problem 4 Evaluation of Curve Realignment versus Design Exception ........................................................................................................... 108 3.3.3 Example Problem 5: Intersection Skew Angle ................................................... 118 3.3.4 Example Problem 6: Deceleration Ramp Lengthening ...................................... 120 3.4 HSM in Operations and Maintenance ..................................................................................... 121 3.4.1 Overview ............................................................................................................ 121 3.4.2 Example Problem 7: Adding Protected Left Turn Phases .................................. 121 3.4.3 Example Problem 8: Work Zone Analysis .......................................................... 122 4 HSM Part D: CMF Applications Guidance ............................................................................. 126 4.1 Overview ................................................................................................................................. 126 4.2 Example Problem 9: Centerline Rumble Strips and Markings ................................................ 126 4.2.1 Introduction ....................................................................................................... 126 4.2.2 Data Requirements ............................................................................................ 126 4.2.3 Analysis .............................................................................................................. 126 4.2.4 Results and Discussion ....................................................................................... 128 4.3 Example Problem 10: Improving Urban Four-Leg Signalized Intersection ............................. 129 4.3.1 Introduction ....................................................................................................... 129 4.3.2 Data Requirements ............................................................................................ 129 4.3.3 Analysis .............................................................................................................. 129 4.3.4 Results and Discussion ....................................................................................... 129 APPENDICES A References ................................................................................................................................... 131 B Glossary ....................................................................................................................................... 132

CONTENTS vi TABLES 1 Application of HSM Part B on Different Stages of Project Development Process ................................. 4 2 HSM Part C Chapters ............................................................................................................................ 10 3 List of SPFs in HSM Part C ..................................................................................................................... 14 4 Roadway Segment and Intersection Types and Descriptions for Rural Two-Lane, Two-Way Roads .................................................................................................................................................... 19 5 Rural Two-Lane, Two-Way Roads SPFs in HSM Chapter 10 ................................................................. 21 6 CMFs for Rural Two-Lane Highway Segments and Intersections ......................................................... 22 7 Overdispersion Parameters for SPFs in HSM Chapter 10 ..................................................................... 24 8 Crash Severity and Collision Type Distribution Table for Different Facility Types ............................... 24 9 Intersection Data Requirements for Rural Two-Lane, Two-Way Roads ............................................... 26 10 Roadway Segment Data Requirements for Rural Two-Lane, Two-Way Roads .................................... 26 11 Roadway Segment and Intersection Types and Descriptions for Rural Two-Lane, Two-Way Roads .................................................................................................................................................... 28 12 Rural Multilane Highways SPFs in HSM Chapter 11 ............................................................................. 30 13 CMFs for Rural Multilane Highway Segments and Intersections ......................................................... 31 14 Chapter 11 SPFs Overdispersion Parameters ....................................................................................... 33 15 Rural Multilane Highway Collision Type Distributions ......................................................................... 33 16 Intersection Data Requirements for Rural Multilane Highways .......................................................... 35 17 Roadway Segment Data Requirements for Rural Multilane Highways ................................................ 35 18 Roadway Segment and Intersection Types and Descriptions for Urban and Suburban Arterials ................................................................................................................................................ 36 19 Urban and Suburban Arterials Facility Types and AADT Ranges .......................................................... 38 20 Urban and Suburban Arterials SPFs in HSM Chapter 12 ...................................................................... 39 21 CMFs for Urban and Suburban Arterials Roadway Segments and Intersections ................................. 40 22 SPFs Overdispersion Parameters in Chapter 12 ................................................................................... 43 23 Urban and Suburban Arterial Crash Severity and Collision Type Distributions ................................... 43 24 Intersection Data Requirements for Urban and Suburban Arterials .................................................... 45 25 Roadway Segment Data Requirements for Urban and Suburban Arterials ......................................... 46 26 Stages of the Project Development Process ........................................................................................ 47 27 Roadway Segments – HSM Table Number for Information on Treatment Summary .......................... 48 28 Intersections – HSM Table Number for Information on Treatment Summary .................................... 49 29 Interchanges – HSM Table Number for Information on Treatment Summary .................................... 50 30 Special Facilities and Geometric Situations – HSM Table Number for Information on Treatment Summary ............................................................................................................................ 50 31 Road Networks – HSM Table Number for Information on Treatment Summary ................................ 51 32 Example Problem 1 – Network Screening Process – Intersection and Roadway Segment Rankings ............................................................................................................................................... 54 33 Example Problem 1 – Contributing Factors and Selected Safety Countermeasures ........................... 56 34 Example Problem 1 – Proposed Projects Benefit-Cost Ratio ............................................................... 57 35 Example Problem 1 – Incremental BCR Analysis .................................................................................. 58 36 Example Problem 1 – Ranking Results of Incremental BCR Analysis ................................................... 59 37 Example Problem 2 – Intersections Input Data .................................................................................... 63 38 Example Problem 2 – Roadway Segment Input Data ........................................................................... 64 39 Example Problem 2 – Intersection 3 Multiyear Analysis Results ......................................................... 66 40 Example Problem 2 – Roadway Segment 2 Multiyear Analysis Results ............................................... 69 41 Example Problem 2 – Corridor Predicted Average Crash Frequency ................................................... 70

CONTENTS vii 42 Example Problem 2 – Predicted and Expected Crash Frequency Calculations Summary (2008 to 2012) ...................................................................................................................................... 72 43 Example Problem 2 – Roadway Segment Alternatives Input Data ...................................................... 74 44 Example Problem 2 – Intersection Alternatives Input Data ................................................................. 75 45 Example Problem 2 – Alternatives Analysis Results Summary............................................................. 76 46 Example Problem 2 – Intersections Input Data .................................................................................... 77 47 Example Problem 2 – Roadway Segment 1 Input Data ........................................................................ 78 48 Example Problem 2 – Intersection 1 Multiyear Analysis Results ......................................................... 80 49 Example Problem 2 – Roadway Segment 1 Multiyear Analysis Results ............................................... 82 50 Example Problem 2 – Corridor Predicted Average Crash Frequency ................................................... 83 51 Example Problem 2 – Year 2030 AADT for Rural Two-Lane and Rural Multilane Facilities ................. 84 52 Example Problem 2 – Future Conditions Alternative Analysis Summary (2030) ................................. 85 53 Example Problem 3 – Intersections Input Data .................................................................................... 87 54 Example Problem 3 – Disaggregated Intersection Crash Data for the Study Period ........................... 88 55 Example Problem 3 – Arterial Roadway Segment Input Data .............................................................. 89 56 Example Problem 3 – Disaggregated Roadway Segment Crash Data for the Study Period ................. 89 57 Example Problem 3 – Intersection 1 Multiyear Analysis Results ......................................................... 95 58 Example Problem 3 – Roadway Segment 1 Multiyear Analysis Results ............................................. 100 59 Example Problem 3 – Corridor Predicted Average Crash Frequency ................................................. 101 60 Example Problem 3 – Disaggregated Roadway Segment and Intersection Crash Data for the Study Period (2008 to 2012) .............................................................................................................. 102 61 Example Problem 3 – Predicted and Expected Crash Frequency Calculations Summary (2008 to 2012) .................................................................................................................................... 103 62 Example Problem 3 – Predicted Pedestrian and Bicycle Average Crash Frequency (2008 to 2012) .................................................................................................................................... 104 63 Example Problem 3 – Corridor Predicted and Expected Crash Frequencies ...................................... 104 64 Example Problem 3 – Intersection Alternatives Input Data ............................................................... 106 65 Example Problem 3 – Roadway Segments Alternatives Input Data ................................................... 106 66 Example Problem 3 – Alternative Analysis Summary Results ............................................................ 107 67 Example Problem 4 – Curve Segments Input Data ............................................................................. 109 68 Example Problem 4 – Roadway Segment 1 Multiyear Analysis Results ............................................. 113 69 Example Problem 4 – Roadway Segment 2 Multiyear Analysis Results ............................................. 113 70 Example Problem 4 – Predicted, Expected, and Observed Crash Frequency Calculations Summary (2008 to 2012) .................................................................................................................... 116 71 Example Problem 4 – Predicted, Expected, and Observed Crash Frequency Calculations Summary for the Three Scenarios (2008 to 2012) ............................................................................. 117 72 Example Problem 4 – Analysis Results Summary ............................................................................... 117 73 Example Problem 9 – CMF Applications – Centerline Markings ........................................................ 127 74 Example Problem 9 – CMF Applications – Centerline Rumble Strips Part 2 ...................................... 127 75 Example Problem 10 – Intersection Treatment Summary ................................................................. 129

CONTENTS viii FIGURES Figure 1: Stability of Performance Measures................................................................................................ 6 Figure 2: Scenarios for HSM Predictive Method Application...................................................................... 11 Figure 3: HSM Part C Chapters and Facility Types ...................................................................................... 11 Figure 4: Illustration of Observed, Predicted, and Expected Crash Frequency Estimates .......................... 13 Figure 5: Sample SPF – Colorado Department of Transportation (Source: Kononov, 2011) ...................... 14 Figure 6: Predictive Method Main Concepts .............................................................................................. 18 Figure 7: Rural Two-Lane, Two-Way Road .................................................................................................. 19 Figure 8: Rural Two-Lane, Two-Way Roads Facility Types and Definitions ................................................ 20 Figure 9: Rural Two-Lane, Two-Way Roads – Definition of Roadway Segments and Intersections ........... 20 Figure 10: Rural Two-Lane, Two-Way Roads Base Conditions.................................................................... 22 Figure 11: Flowchart for Calculating Expected Crash Frequency on Rural Two-Lane, Two-Way Roads .... 25 Figure 12: Rural Multilane Highways .......................................................................................................... 27 Figure 13: Multilane Rural Roads Facility Types and Definitions ................................................................ 28 Figure 14: Rural Multilane Highways – Definition of Roadway Segments and Intersections ..................... 29 Figure 15: Rural Multilane Highway Base Conditions ................................................................................. 30 Figure 16: Flowchart for Calculating Predicted and Expected Crash Frequency on Rural Multilane Highways ................................................................................................................................... 34 Figure 17: Urban and Suburban Arterials Facility Types and Definitions ................................................... 37 Figure 18. Urban and Suburban Arterials – Definition of Roadway Segments and Intersections .............. 38 Figure 19: Urban and Suburban Arterials Base Conditions ......................................................................... 40 Figure 20: Flowchart for Calculating Expected Crash Frequency on Urban and Suburban Arterials ......... 44 Figure 21: Available Performance Measures (HSM Table 4-2 [HSM p. 4-9]) .............................................. 54 Figure 22: State Route Rural Two-Lane, Two-Way Road ............................................................................ 62 Figure 23: Example Problem 1 – Sample Rural Two-Lane, Two-Way Road ................................................ 63 Figure 24: Example Problem 1 – Sample Rural Multilane Highway ............................................................ 77 Figure 25: Sample Urban and Suburban Arterial ........................................................................................ 86 Figure 26: Example Problem 2 – Project Alternatives .............................................................................. 105

ix Abbreviations and Acronyms 2U two-lane undivided arterials 3SG signalized three-leg intersections 3ST three-leg intersection with stop control 3T three-lane arterials 4D divided four-lane roadway segments 4SG four-leg signalized intersection 4ST four-leg intersection with stop control 4U undivided four-lane roadway segment 5T five-lane arterials AASHTO American Association of State Highway and Transportation Officials AASHTO Redbook A Manual of User Benefit Analysis for Highway and Bus-Transit Improvements AADT average annual daily traffic AADTmajor average annual daily traffic on the major route AADTminor average annual daily traffic for the minor route BCR benefit-cost ratio Ci intersection calibration factor Cr segment calibration factor CMF crash modification factor DOT Department of Transportation EB Empirical Bayes(ian) EEACF excess expected average crash frequency FHWA Federal Highway Administration FI fatal-and-injury GIS geographic information system HFG Human Factors Guide HOV high-occupancy vehicle HSIP Highway Safety Improvement Program HSM Highway Safety Manual ID identification number IHSDM Interactive Highway Safety Design Model Int intersection

ABBREVIATIONS AND ACRONYMS x k overdispersion parameter KABCO Five-level injury severity scale. K – fatal injury; A – incapacitating injury; B – non-incapacitating evident injury; C – possible injury; O – property damage only mph miles per hour MSE multiple of standard error NCHRP National Cooperative Highway Research Program NPV net present value N number PDO property damage only PV present value RHR roadside hazard rating RTM regression- to-the-mean RTOR right-turn-on-red SE standard error Seg segment SPF safety performance function SR State Route TRB Transportation Research Board TWLTL two-way left-turn lane vpd vehicles per day w weighting factor

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The Highway Safety Manual can be used to identify sites with the most potential for crash frequency or severity reduction; identify contributing factors to crashes and mitigation measures; and estimate the potential crash frequency and severity on highway networks, among other uses.

The TRB National Cooperative Highway Research Program's NCHRP Web-Only Document 323: Highway Safety Manual User Guide is a user-friendly, companion and reference document that helps safety analysts use the Highway Safety Manual.

Supplemental to the document are three Peer Exchange Reports from Irvine, California; Baltimore, Maryland; and Nashville, Tennessee; and three Tech Briefings (1, 2, and 3).

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