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NCHRP Web-Only Document 377 Background and Development of a Guide for Intersection Control Evaluation Bastian Schroeder Burak Cesme Kaitlyn Schaffer Paul Ryus Shannon Warchol Sarah Brown Sophia Semensky Nagui Rouphail Kittelson & Associates, Inc. Wilmington, NC Jonathan Reid Arcadis Raleigh, NC Joanna Reagle Justin Ferry Karen Jehanian KMJ, Inc. Ardmore, PA Charles Brown Equitable Cities LLC Somerset, NJ Conduct of Research Report for NCHRP Project 17-98 Submitted September 2023 © 2023 by the National Academy of Sciences. National Academies of Sciences, Engineering, and Medicine and the graphical logo are trademarks of the National Academy of Sciences. All rights reserved. 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 techniquesâthe 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 Transportation Research Board does not develop, issue, or publish standards or specifications. The Transportation Research Board manages applied research projects which provide the scientific foundation that may be used by Transportation Research Board sponsors, industry associations, or other organizations as the basis for revised practices, procedures, or specifications. The Transportation Research Board, the National Academies, and the sponsors of the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturersâ names appear herein solely because they are considered essential to the object of the report. The information contained in this document was taken directly from the submission of the author(s). This material has not been edited by TRB.
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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 WEB-ONLY DOCUMENT 377 Waseem Dekelbab, Deputy Director, Cooperative Research Programs, and Manager, National Cooperative Highway Research Program Amir N. Hanna, Senior Program Officer Emily Griswold, Senior Program Assistant Natalie Barnes, Director of Publications Heather DiAngelis, Associate Director of Publications Jennifer J. Weeks, Publishing Projects Manager NCHRP PROJECT 17-98 PANEL Field of TrafficâArea of Safety Michelle Nickerson, Tennessee Department of Transportation, Nashville, TN (Chair) Nithin K. Agarwal, University of Florida, Gainesville, FL Marcus H. Januario, Shive-Hattery (formerly), Cedar Rapids, IA Angela J. Kargel, Oregon Department of Transportation, Salem, OR Sanhita Lahiri, Virginia Department of Transportation, Richmond, VA Tobey Reynolds, New Hampshire Department of Transportation, Concord, NH Stuart Samberg, Rummel, Klepper, and Kahl, LLP (RK&K), Glen Allen, VA Kevin Scopoline, Wisconsin Department of Transportation, Madison, WI James S. Sullivan, Mississippi Department of Transportation, Jackson, MS Hillary Nicole Isebrands, FHWA Liaison AUTHOR ACKNOWLEDGMENTS The research reported herein was performed under NCHRP Project 17-98, âGuide for Intersection Control Evaluation,â by Kittelson & Associates, Inc.; Arcadis; KMJ, Inc; and Equitable Cities LLC. Kittelson & Associates, Inc., was the contractor for this study. The work undertaken by other project team members occurred under subcontracts with Kittelson & Associates, Inc. Bastian Schroeder, PhD, PE, of Kittelson & Associates, Inc., was the principal investigator. The other authors of this report were Burak Cesme, PhD; Kaitlyn Schaffer; Paul Ryus; Shannon Warchol; Sarah Brown; Sophia Semensky; and Nagui Rouphail, PhD, of Kittelson & Associates, Inc. For subcontractor Arcadis, the lead investigator and author was Jonathan Reid, PE, PTOE, RSP. For subcontractor KMJ, Inc, the contributing authors were Joanna Reagle, Justin Ferry, and Karen Jehanian. For subcontractor Equitable Cities LLC, the key author was Charles Brown. The project team acknowledges the contributions of representatives from various state departments of transportation who responded to the project outreach survey about their processes for intersection control evaluation and provided helpful insights to the project team.
iv Table of Contents LIST OF FIGURES ..................................................................................................................... vi LIST OF TABLES ...................................................................................................................... vii SUMMARY ................................................................................................................................ viii Introduction ........................................................................................................................................... viii State of the Practice ............................................................................................................................... viii Recommended ICE Processes ................................................................................................................. ix New and Enhanced Evaluation Methods for ICE Processes ................................................................. xiii Development of a Guide to Intersection Control Evaluation ................................................................. xv Conclusions .......................................................................................................................................... xvii CHAPTER 1: BACKGROUND .................................................................................................. 1 Overview .................................................................................................................................................. 1 Terminology ............................................................................................................................................. 2 CHAPTER 2: STATE OF THE PRACTICE ............................................................................. 3 Introduction .............................................................................................................................................. 3 Summary of State DOT ICE Processes .................................................................................................... 4 Intersection Concepts Analysis Literature .............................................................................................. 11 Agency Practice Review ......................................................................................................................... 16 Factors for Intersection Control Evaluation ........................................................................................... 19 CHAPTER 3: RESEARCH APPROACH ................................................................................ 33 Introduction ............................................................................................................................................ 33 ICE Evaluation Factors and Methods Assessment ................................................................................. 33 Draft Framework for Developing ICE .................................................................................................... 42 Gap-Filling and Focused Research ......................................................................................................... 47 CHAPTER 4: FINDINGS AND APPLICATIONS ................................................................. 53 Recommended ICE Processes ................................................................................................................ 53 ICE Stage 1 Safety Screening Method ................................................................................................... 56 Stage 1 Pedestrian and Bicyclist Safety Method for ICE ....................................................................... 72 Planning-Level Capacity Methods for Additional Intersection Types ................................................... 94 Integrating Social Equity in ICE .......................................................................................................... 102 CHAPTER 5: CONCLUSIONS AND SUGGESTED RESEARCH .................................... 119 Conclusions .......................................................................................................................................... 119 Suggested Research .............................................................................................................................. 120 REFERENCES .......................................................................................................................... 122
v APPENDIX A: SUMMARY OF STATE DOT ICE PROCESSES ..................................... A-1 Introduction .......................................................................................................................................... A-1 State DOT Summaries .......................................................................................................................... A-1 APPENDIX B: DETAILS OF PLANNING-LEVEL METHODS FOR INNOVATIVE INTERSECTIONS AND INTERCHANGES ........................................................................ B-1 Overview .............................................................................................................................................. B-1 Restricted Crossing U-Turn Intersection (RCUT) ................................................................................ B-2 Median and Partial Median U-Turns (MUT and PMUT) ..................................................................... B-5 Diverging Diamond Interchange (DDI) ................................................................................................ B-7 Partial Continuous Flow Intersection (CFI) ......................................................................................... B-9 Bowtie Intersection ............................................................................................................................. B-11 Quadrant Roadway Intersection (QRI) ............................................................................................... B-15 Forward and Reverse Jughandle Intersections (FJI and RJI) ............................................................. B-17 Continuous Green T-Intersection (CGT) ............................................................................................ B-21 APPENDIX C: CASE STUDIES ............................................................................................. C-1 SR 241 and Rocherty Road, Lebanon County, PA ............................................................................... C-1 198th Avenue and Old Highway 99, Grand Mound, WA .................................................................... C-2 I-41/Wisconsin 47 Interchange, Appleton, WI ..................................................................................... C-4 US 12/18 at Millpond Road and County Road AB, Madison, WI ....................................................... C-5 Wisconsin 54 at Main Street and Ivory Street, Seymour, WI ............................................................... C-7 SR 108/49 and Mackey Ranch Road, Jamestown, CA ......................................................................... C-8 US 92 and Tomoka Farms Road, Daytona Beach, FL.......................................................................... C-9 Minton Road Corridor, Brevard County, FL ...................................................................................... C-11 Oregon 47 at Maple Street/Fern Hill Road, Forest Grove, OR .......................................................... C.12 I-95/Chichester Avenue Interchange, Upper Chichester, PA ............................................................. C-14 TH 97 at Goodview Avenue/8th Street, Forest Lake, MN ................................................................. C-15 I-35/TH 33 Interchange, Cloquet, MN ............................................................................................... C-16 APPENDIX D: CASE STUDY APPLICATIONS ................................................................. D-1 Overview .............................................................................................................................................. D-1 Vehicular Safety Methods .................................................................................................................... D-1 Pedestrian and Bicyclist Safety Screening Methods............................................................................. D-3 Cost Evaluation Methods ...................................................................................................................... D-6 Vehicle Mobility Methods .................................................................................................................... D-7 NCHRP Web-Only Document 377 contains the Conduct of Research Report for NCHRP Project 17-98 and accompanies NCHRP Research Report 1087: Guide for Intersection Control Evaluation. Readers can read or purchase NCHRP Research Report 1087 on the National Academies Press website (nap.nationalacademies.org).
vi List of Figures Figure 1. Elements of the 8-S ICE Framework. ............................................................................................ x Figure 2. Recommended ICE Stage 1 and Stage 2 Steps. ........................................................................... xii Figure 3. Performance-Based Approach. .................................................................................................... 21 Figure 4. Draft Framework for Developing an ICE Process. ...................................................................... 43 Figure 5. Defining the Scale of ICE. ........................................................................................................... 43 Figure 6. Defining Spatial Scope in ICE. .................................................................................................... 44 Figure 7. Defining Contextual Scope in ICE. ............................................................................................. 45 Figure 8. Defining Steps in ICE (Safety Example). .................................................................................... 46 Figure 9. Defining Sequence in ICE â Multiple Options. ........................................................................... 46 Figure 10. Evaluation Concept for Stage 1 and 2 Methods. ....................................................................... 52 Figure 11. Steps in the 8-S ICE Framework. .............................................................................................. 53 Figure 12. Recommended ICE Stage 1 and Stage 2 Steps. ......................................................................... 55 Figure 13. Screenshot of Florida DOT SSI Calculator. .............................................................................. 58 Figure 14. VJuST Conflict Point Method Applied to a Median U-Turn (MUT) Intersection. ................... 59 Figure 15. Screenshot of FHWA SPICE Tool Analysis Results. ............................................................... 61 Figure 16. Vehicular Conflict Points Defined for a Median U-Turn Intersection. ..................................... 65 Figure 17. Diagram Illustrating Various Angles of Collision. .................................................................... 66 Figure 18. Example of Merging Movement with Merging Weights Defined for Left-turn Conflict Point. ....................................................................................................................................... 68 Figure 19. Screenshot of FHWA CAP-X Ped/Bike Safety Spreadsheet. .................................................... 72 Figure 20. Screenshot of FDOT Cap-X Bike/Ped Safety Spreadsheet. ...................................................... 73 Figure 21. Screenshot of Colorado DOT's ICAT Spreadsheet with Multimodal Safety Questions. .......... 74 Figure 22. Screenshot of Ohio DOT CAP-X Bicycle Safety Worksheet. ................................................... 75 Figure 23. Crosswalk Marking Legend. ...................................................................................................... 78 Figure 24. Assumed Crossing Assignments, Conflicting Vehicle Types, and Marking Types for a TWSC Intersection. ................................................................................................................. 78 Figure 25. Example of Multimodal Ped Worksheet Inputs. ........................................................................ 79 Figure 26. Reset Default Values Button. .................................................................................................... 79 Figure 27. Example of Roadway Speeds Inputs. ........................................................................................ 80 Figure 28. Example of Out-of-Direction Travel at a Partial DLT Intersection. .......................................... 81 Figure 29. Northwest-to-Southeast Quadrant Multistage Crossing at an RCUT. ....................................... 82 Figure 30. Risk of Severe Injury by Impact Speed. .................................................................................... 84 Figure 31. Default (a) and Modified (b) Crossing Locations and Markings for a Traffic Signal. .............. 86 Figure 32. Default Inputs for a Traffic Signal............................................................................................. 86 Figure 33. Modified Inputs for a Traffic Signal. ......................................................................................... 86 Figure 34. Facility Type Input. ................................................................................................................... 88 Figure 35. Roadway Speed Inputs. ............................................................................................................. 88 Figure 36. Preferred Bikeway Type for Urban, Urban Core, Suburban, and Rural Town Contexts. ......... 91 Figure 37. Bicycle Level of Traffic Stress Criteria for Road Segments. .................................................... 92 Figure 38. Conflict Area Designations for the South Approach Movements. ............................................ 96 Figure 39. Four-Node Designation of Movement O-Ds at Innovative Intersections. ................................. 98 Figure 40. General Computational Framework for New Planning-Level Methods. ................................... 99 Figure 41. Aerial Photo of Case Study Intersection. ................................................................................. 108 Figure 42. Future Land Use Designations in Intersection Vicinity. ......................................................... 109 Figure 43. Historical Development of the Intersection Vicinity. .............................................................. 111 Figure 44. Census Block Groups Forming the Case Study Focus Area. .................................................. 113
vii List of Tables Table 1. State-by-State Overview of ICE Processes. .................................................................................... 4 Table 2. State-by-State ICE Process Inputs and Outputs. ............................................................................. 7 Table 3. Frequency of Use of ICE Inputs. .................................................................................................. 11 Table 4. Factors to Consider in ICE. ........................................................................................................... 23 Table 5. Methods to Quantify Most Common Factors for ICE. ................................................................. 25 Table 6. Methods to Quantify Often-Used Factors for ICE. ....................................................................... 25 Table 7. Methods to Quantify Emerging Factors for ICE. .......................................................................... 26 Table 8. Evaluation of ICE Factors. ............................................................................................................ 34 Table 9. Summary of Methods for Testing. ................................................................................................ 52 Table 10. Safest Feasible Intersection Design Table Based on all Crashes. ............................................... 60 Table 11. Enhanced Safety Screening Method for Stage 1 of ICE Analysis Results from the Sample Locations. ................................................................................................................... 62 Table 12. Factors Used to Evaluate Ease of Method Incorporation into ICE Processes. ........................... 63 Table 13. Measure Evaluation Framework Applied to ICE Stage 1 Safety Methods. ................................ 63 Table 14. Criteria for New Stage 1 Safety Method. .................................................................................... 64 Table 15. Modified SSI Method Inputs. ..................................................................................................... 65 Table 16. Regression Parameters as Computed by Evans (1994). .............................................................. 67 Table 17. Pedestrian Optimum Feasible Intersection Design (POFID) Table. ........................................... 76 Table 18. Bicycle Optimum Feasible Intersection Design (BOFID) Table. ............................................... 76 Table 19. Measure Evaluation Framework Applied to Ped/Bike Stage 1 Screening Method. ................... 77 Table 20. Number of Lanes Factor Score (FL). ........................................................................................... 83 Table 21. Vehicle Speed Score. .................................................................................................................. 84 Table 22. Vehicle Volume and Conflicting Vehicle Control Type Score. ................................................. 85 Table 23. Presence of Markings Score. ....................................................................................................... 85 Table 24. Out-of-Direction Travel Score. ................................................................................................... 85 Table 25. Multistage Crossing Score. ......................................................................................................... 85 Table 26. Facility Type, Leg AADT, and Roadway Speed Score for Shared-Use Path Facilities. ............ 90 Table 27. Facility Type, Leg AADT, and Roadway Speed Score for On-Street Lane Facilities. .............. 91 Table 28. Facility Type, Leg AADT, and Roadway Speed Score for Facilities Shared with Vehicles. .................................................................................................................................. 91 Table 29. Number of Adjacent Through Lanes Score. ............................................................................... 93 Table 30. Conflicting Control Type Score. ................................................................................................. 93 Table 31. Out-of-Direction Travel Score. ................................................................................................... 93 Table 32. Riding Between Travel Lanes Score. .......................................................................................... 93 Table 33. Riding Across Free-Flow Ramp Score. ...................................................................................... 94 Table 34. Existing and Gap-Filling Methods for Mobility Assessment. .................................................... 95 Table 35. Case Study Focus Area Racial Demographics. ......................................................................... 113 Table 36. Case Study Focus Area Hispanic and Latin(o/a/x) Demographics. .......................................... 114 Table 37. Case Study Focus Area Population with a Disability. .............................................................. 114 Table 38. Case Study Focus Area Ratio of Household Income to Poverty. ............................................. 114 Table 39. Case Study Focus Area Age Profile. ......................................................................................... 115 Table 40. Case Study Focus Area Population without a Vehicle. ............................................................ 115 Table 41. Example Social Equity Needs Summary. ................................................................................. 116
viii Summary Introduction A variety of intersection control evaluation processes and metrics are used by highway agencies for evaluating intersection geometry and control options and identifying an optimal geometric and control solution for an intersection. These processes usually address safety, operational, multimodal, environmental, right-of-way, and cost impacts and other considerations. However, there is no widely accepted procedure or guide for evaluating new intersections or modifications to an intersection. NCHRP Project 17-98âs objective was to develop such a guide, along with associated processes, performance metrics, and tools to provide consistent and objective intersection control evaluation (ICE). This report documents the research conducted during NCHRP Project 17-98 and addresses the following topics: ⢠A review of the state of the practice as of 2021 ⢠The development of recommended practices for (1) developing and implementing an ICE process within a transportation agency, and (2) conducting an ICE analysis ⢠The development of new and enhanced evaluation methods for ICE processes to allow a greater range of intersection forms and evaluation criteria to be incorporated into ICE processes: o Enhanced screening methods for vehicular, pedestrian, and bicyclist safety o New planning-level traffic operations evaluation methods for all-way stop and innovative intersection and interchange forms o A new method for evaluating social equity within an ICE analysis ⢠Twelve case study examples of how state DOTs have applied ICE to a range of intersection and interchange evaluations; ten of these were also used to test new and enhanced evaluation methods ⢠The development of NCHRP Research Report 1087: Guide for Intersection Control Evaluation and its accompanying spreadsheet tools. State of the Practice The state of the practice was determined through a combination of a literature review, outreach to the ten state departments of transportation (DOTs) with existing ICE processes as of May 2021, and outreach to other state DOTs in the process of developing ICE processes, as well as those without any active ICE- related activity. The literature review highlighted many similarities in the motivations, processes, and evaluation methods and factors among the statesâ ICE guidelines. ICE guidelines were developed to provide consistent documentation in the selection of intersection form and control and to expand the types of intersections being evaluated. ICE has helped state DOTs promote roundabouts and other innovative intersection designs to leverage safety advancements. Most states that have ICE guidelines have multistage ICE processes that first screen intersection configurations for feasibility and then compare the feasible concepts to select the most appropriate intersection form and control. The most appropriate concept is determined using several evaluation factors. Common evaluation factors include traffic operations and safety performance, which are evaluated using a variety of methods including state-developed spreadsheet tools. The tools also evaluate factors, such as pedestrian and bicycle accommodations, public input, environmental impacts, and cost. Benefitâcost
ix analysis is a common method used to objectively compare the concepts. The level of detail and documentation required to complete an ICE is dependent on the state. Some statesâ guidelines provide more flexibility whereas other statesâ guidelines are extremely explicit in the requirements to complete an ICE. Additionally, many states and research entities have explored various processes to evaluate, analyze, and select intersection concepts. They have created tools and use variables and methodologies that are similar to many of those required in statesâ ICE guidelines. Variables included evaluations of safety, operations, access management, exposure, conflict point severity, kinetic energy management, pedestrian/bicycle accommodations, maintenance, and others. Methods include costâbenefit analysis, safety index methods, microsimulation, critical lane analysis, safety performance analysis, and others. Other notable work included Safe Systems principles and systemic safety approaches integrated into concept selection, NCHRP synthesis research for innovative intersection analysis and design, and research on public involvement and education for intersection concepts. The following key takeaways regarding ICE policies and processes were identified from the agency outreach: ⢠Training and education are of paramount importance. Reluctant adopters and those unfamiliar with ICE will not voluntarily select an alternative to a signalized intersection, even if it fits the situation better. Similarly, if the public does not understand the advantages of an innovative intersection, there will be additional friction during public meetings and less overall acceptance and enthusiasm. ⢠Codifying ICE policy and integrating it in a consistent fashion into the design process is one of the largest predictors of success. ⢠Implementing ICE policy early in the project (during scoping) seems to avoid issues down the line â in cost, design time, and public acceptance. ⢠States without an ICE policy have frameworks for evaluating intersection control, similar to states with ICE policies, but the frameworks are not as robust, not taking into account many of the factors identified in the literature. ⢠The biggest drivers for states developing ICE policies are safety and efficiency concerns, as well as developing a standardized process. ⢠FHWA support and encouragement of states to develop ICE policies was important, based on responses from states currently in the process and those that that had previously adopted ICE policies. Recommended ICE Processes The research identified steps needed to develop and implement an agency ICE process and recommended specific evaluation criteria, performance metrics, analysis tools, and documentation requirements to incorporate into an ICE process. Developing an ICE Process This report documents the initial development and evolution of the guidance for developing an ICE process that is presented in NCHRP Research Report 1087: Guide for Intersection Control Evaluation. The final version of the guidance consists of the eight-element process illustrated in Figure 1. Each of the frameworkâs eight elements starts with the letter âSâ and the framework is therefore referred to as the â8-S Framework.â The first element, Start-Up, incorporates steps typically used when initiating any new agencywide process. The next three elements, Style, Scale, and Scope, are policy-related elements that establish the broad parameters of where, when, and how much ICE will be applied. The final four elements, Stages, Steps, Sequence, and Selection, establish the details of the ICE process and determine how ICE relates to other agency processes.
x Figure 1. Elements of the 8-S ICE Framework. Each element in the framework contains a series of questions that the agency should answer before moving to the next element. Answers to questions in earlier framework elements will influence decisions made in later elements. For example, the questions related to âStyleâ consist of: ⢠What is the desired level of effort? ⢠Who will apply the ICE process (agency staff, consultants, or both)? ⢠Who will pay for ICE evaluations (the agency, a public or private organization proposing to construct or modify an intersection on an agency-owned roadway, or cost sharing)? The recommended ICE process summarized in the next subsection answers these questions by default, but agencies are free to adapt the recommended process to fit their own needs and should consider whether each default answer is the most appropriate answer for them. Other state DOTâs existing ICE processes can also be used for inspiration. Applying ICE This report also documents the initial development and testing of the projectâs recommended ICE process presented in NCHRP Research Report 1087: Guide for Intersection Control Evaluation. Guiding Principles The research team applied the following principles in developing the recommended ICE process. General Format of ICE ⢠The recommended process incorporates two evaluation stages, similar to what many states with ICE processes have adopted. While some states also use a third stage, that stage does not appear to provide significant value over an iteration in Stage 2. Similarly, states with a single stage ICE process still use multiple steps to further screen and filter options. ⢠Some evaluation factors would be considered only in Stage 1 or only in Stage 2, while others would be included in both stages, but evaluated at a much lower level of detail during Stage 1.
xi Principles for ICE Stage 1 ⢠In Stage 1, land use context (e.g., context classification, key adjacent land uses such as elementary school, senior center, school for the blind) and corridor context (e.g., roundabout corridor, coordinated signal system, dedicated transit facilities, AADT, median presence, number of lanes approaching intersection) is used to identify an initial set of potentially feasible configurations and/or to screen out configurations. For example, this process would eliminate a high-capacity displaced left-turn intersection at a rural intersection of two 2-lane roads. ⢠The primary purpose of Stage 1 is to filter or eliminate certain configurations with minimal quantitative effort. The goal is to reduce the number of configurations subjected to a more detailed assessment in Stage 2. ⢠Stage 1 also identifies potential constraints (e.g., available right-of-way, terrain, known wetlands, adjacent intersections and driveways, policy, budget). The agency or user would have to decide what creates a sufficiently large constraint to screen out a configuration (e.g., need to purchase any right- of-way, need to purchase already developed right-of-way). ⢠The steps in Stage 1 are sequenced to reach a smaller, feasible set of configurations fairly quickly, since the intent is not to select any particular configuration, but rather to determine which configurations will be carried forward. ⢠Screening can occur on a pass/fail basis (e.g., right-of-way) or on the basis of not meeting the project objectives specified in the context statement (e.g., project motivated by safety concerns, but the configuration would not reduce crash frequency or severity). Principles for ICE Stage 2 ⢠The Stage 2 process is quantitative and uses both existing and newly developed analysis tools to permit the analysis of additional types of intersection configuration, and to include effects on multimodal users. In addition, high-level cost estimates and environmental impacts are carried out. ⢠The process relies on existing tools to the extent possible, but includes new methods or refinements within them as needed to analyze particular intersection forms and quantify particular evaluation factors. Framework of the Recommended Processes Figure 2 presents the steps included in the recommended Stage 1 and Stage 2 processes presented in NCHRP Research Report 1087: Guide for Intersection Control Evaluation. Within each step, the guidance presents the data needed for that step and key questions being asked. For example, for Step 1.1, High-Level Equity Assessment, the data needs are information about travel modes and patterns and a review of how the intersection and its surroundings has developed. Key questions asked in this step are: ⢠What are the surrounding land uses, and do they differ by the side of the road? ⢠What travel modes are present, or likely to be present, at the study location? ⢠What are the likely travel needs for users of each mode? ⢠How have the surrounding neighborhoods and the major road developed over time?
xii Figure 2. Recommended ICE Stage 1 and Stage 2 Steps and Tools Key elements of each step are the following: ⢠Step 1.0: Initiate ICE Process. Does the study intersection meets the criteria established in the ICE process for performing an ICE analysis? If ICE is not applicable to the project, no further analysis is needed. If ICE is applicable, the process continues to Step 1.1. ⢠Step 1.1: High-Level Equity Assessment. This step is designed to develop an understanding of the intersectionâs role in the community, to ensure that the needs of all travel modes are considered throughout the ICE process, to develop information that will inform how different evaluation factors will be weighted in Stage 1 and 2 analyses, and to identify design elements that should be incorporated into all design concepts developed during Stage 2. ⢠Step 1.2: Initial Context and Feasibility Assessment. This step uses basic intersection information to eliminate intersection types that are infeasible given traffic volumes (e.g., providing too much or not enough capacity) and project context (e.g., grade separations in an urban core). The outcome of
xiii this step is an initial list of feasible intersection configurations that can be evaluated further. The ICE Process Tool developed by this project largely automates this step. ⢠Step 1.3: Develop Initial Configurations. This step identifies high-level configurations for each feasible intersection type, which take only a few minutes to prepare. The main characteristic that needs to be determined for each intersection type is the lane configuration. ⢠Step 1.4: Stage 1 Analysis. This step includes volume-to-capacity ratio screening, a pedestrian and bicyclist safety assessment, motor vehicle safety screening, environmental screening, and high-level cost screening. Spreadsheet tools are used for four of these analyses, with the environmental screening being a high-level review of apparent impacts to environmental and community resources. ⢠Step 1.5: Stage 1 Results and Fast Tracking. This step narrows the feasible configurations down to a prioritized list of intersection concepts without fatal flaws and selects which concepts will advance to Stage 2. In some cases, only one feasible concept will remain, in which case Stage 2 is skipped. In other cases, a fatal flaw can be mitigated by revising the assumptions used in developing the initial configuration, in which case Step 1.4 is repeated for that configuration and the Step 1.5 rankings revised as needed. ⢠Step 2.0: Initiate ICE Stage 2. ICE Stage 2 is initiated when ICE Stage 1 is completed and there is more than one feasible intersection form for the project location. The first step of Stage 2 is to review the feasible concepts developed in Stage 1 and the performance results of those concepts before proceeding with further analysis. ⢠Step 2.1: Detailed Equity and Context Assessment. This step applies the information developed during Stage 1 to support later steps in Stage 2, such as concept design. Optionally, this step can conduct a more detailed demographic evaluation of the area surrounding the intersection, to identify the need for more than the minimum level of facilities (particularly those serving persons walking, including persons with disabilities) that may not be apparent from the Stage 1 evaluation. This step can also include an optional public outreach process to gather stakeholder and public input on the intersection concepts being considered. ⢠Step 2.2: Develop Concepts. This step develops conceptual designs for each intersection concept. These designs are essential for communicating differences in intersection concepts to the public and for evaluating site-specific factors such as cost, right-of-way impact, and environmental impact. ⢠Step 2.3: Stage 2 Analysis. This step conducts detailed evaluations of vehicle delay, pedestrian and bicyclist safety, vehicular safety, construction cost, life-cycle cost, and environmental impacts using a variety of analysis tools. ⢠Step 2.4: Stage 2 Results and Ranking. The concepts are ranked based on the results of Step 2.3 and the evaluation factor weights developed in Stage 1. This process may require a few iterations before the selection is finalized. Analysts can revise the concepts based on the outcomes of the initial analysis. Ultimately, the rank allows analysts to select a preferred intersection concept to continue into project planning and preliminary engineering activities. New and Enhanced Evaluation Methods for ICE Processes ICE Stage 1 Vehicular Safety Screening Method The research team applied three existing vehicular safety screening methodsâVirginia DOTâs VJuST, North Carolina DOTâs SaFID, and FHWAâs SSIâto case study locations and compared the methodsâ results to those from FHWAâs more detailed SPICE method. The methods were also evaluated in terms of their ease of use within an ICE process. Based on this assessment, the developed a modified version of the SSI method that has three primary differences from the current method: ⢠Expanded the method and computational tool to work for grade-separated interchanges in addition to at-grade intersections
xiv ⢠Modified the method to remove the multimodal conflict score, because multimodal safety is assessed separately in this projectâs recommended ICE framework ⢠Enhanced the method and computation tool to include conflict diagrams similar to the VJuST method, to visually convey the type and SSI-estimated severity of each conflict at the intersection or interchange. ICE Stage 1 Pedestrian and Bicyclist Safety Screening Methods The research team applied five existing pedestrian and bicyclist safety screening methodsâFHWA, Florida DOT, and Ohio DOT implementations of CAP-X; Colorado DOTâs ICAT; and North Carolina DOTâs POFID and BOFIDâto case study locations and evaluated the methods in terms of their ease of use within an ICE process. Based on this evaluation, the research team moved forward with further testing and development of the Ohio DOT method. This method represents an evolution of prior screening methods used in the FHWA and Florida DOT CAP-X tools by incorporating the concepts and safety relationships for the innovative intersections described in NCHRP Research Report 948 (Kittelson & Associates, Inc. et al. 2020), while being customized to be suitable for a ICE Stage 1 assessment. The computational logic is integrated into the CAP-X spreadsheet, which greatly streamlines its use. Planning-Level Capacity Methods for All-Way-Stop and Innovative Intersections NCHRP Report 825: Planning and Preliminary Engineering Applications Guide (PPEAG) to the Highway Capacity Manual (HCM) (Dowling et al. 2016) includes simplifications of HCM methods for signalized intersections, roundabouts, stop-controlled intersections, and other roadway elements. However, the PPEAG does not contain planning-level methods for evaluating innovative intersections or interchange ramp terminals, even though detailed operational methods for many configurations are provided in the HCM 6th Edition (TRB 2016). To allow ICE analyses to evaluate all potential intersection configurations on an equal footing, the research team developed planning-level methods for innovative intersections based on the existing planning-level method for signalized intersections presented in the PPEAG. The team also updated the PPEAGâs method for all-way stop-controlled intersections by implementing a non-iterative capacity method developed by Wu (2000). The methods for these intersection configurations, along with those originally addressed in the PPEAG, have been implemented in a spreadsheet tool. Integrating Social Equity in ICE Incorporating social equity into ICE is a crucial investment of time and effort. The process helps uncover how and why the intersection and its surroundings have developed over time; who uses the intersection; what travel modes those persons may use; and how an intersection concept could benefit the surrounding communityâs quality of life. A thoughtful and thorough analysis of available data can help shape shared expectations between the community and the ICE project purpose and need, build trust and capacity between stakeholders, and foster more equitable outcomes from the onset of intersection concept selection that will extend beyond the life of the intersection project. The two-stage approach to evaluating social equity developed by the project focuses on developing an understanding of the intersectionâs context and users, and applying this knowledge when weighting evaluation factors and developing intersection concept designs. This process largely incorporates the same types of data used in long-range transportation planning, and the availability of U.S. Census data and online equity calculators make data collection and analysis quite efficient. Stage 1 of the social equity evaluation is designed to develop a basic understanding of the intersection context by developing answers to the following questions:
xv ⢠What are the surrounding land uses? Do they differ by side of the road? ⢠What travel modes are present (or likely to be present) at the study location? ⢠What are the likely travel needs for users of each mode? ⢠How have the surrounding neighborhoods and the major road developed over time? Data sources that can be used to answer these questions include field visits; local pedestrian, bicycle, and transit plans; local zoning and comprehensive plans; current and historical aerial photography and maps (e.g., from online sources); institutional knowledge; and contacts with community and neighborhood groups. Stage 2 of the social equity methodology applies the information developed during Stage 1 to support concept design. Optionally, this stage can conduct a more detailed demographic evaluation of the area surrounding the intersection, to identify the need for more than the minimum level of facilities (particularly those serving persons walking, including persons with disabilities) that may not be apparent from the Stage 1 high-level evaluation. Stage 2 can also include an optional public outreach process to gather stakeholder and public input on the intersection concepts under consideration and use the results as an additional evaluation factor. In the absence of a public outreach effort, concept compatibility with the intersection context could be applied instead as an optional evaluation factor. Many of the potential solutions to making an intersection a community asset rather than a barrier involve providing safe and convenient facilities for persons walking, biking, rolling, and using transit. Incorporating multimodal elements into intersection concepts can help reverse the effects of years of attention to the needs of motor vehicle users and corresponding neglect to the needs of other intersection users. The social equity analysis can also identify multimodal upgrades to an intersection needed when an intersection originally designed to fit one context (e.g., rural) has not evolved over time to match its surrounding context (e.g., suburban). Development of a Guide to Intersection Control Evaluation NCHRP Research Report 1087: Guide for Intersection Control Evaluation presents the recommended ICE processes summarized above. The first four chapters of the guide are process-oriented and are written for roadway agency managers and decision-makers who are considering starting an ICE process or who already have an existing ICE process and are looking for inspiration on ways to improve their process. The remainder of the guide provides details about intersection forms, control types, analysis methods, and analysis tools, and is designed as a reference for roadway agency staff responsible for developing and implementing an ICE process. The guide contains five main chapters: ⢠Chapter 1, Introduction, introduces the ICE concept, describes the benefits of incorporating an ICE process into transportation agency decision-making, and provides examples of transportation agencies that already use ICE. This chapter also defines key ICE-related terms and provides a roadmap to the remainder of the guide. ⢠Chapter 2, Framework for Setting Up ICE, introduces a framework for initiating an ICE process at a state DOT or other roadway agency. Each framework element introduces a set of questions that guide the agency in customizing its process. Questions asked in the earlier elements help shape the big- picture aspects of how the ICE process should function, while the questions asked in later elements flesh out the details of the process. To help agency staff answer these questions, the chapter provides examples of different ways ICE processes can be structured, along with their respective advantages and disadvantages. Chapter 2 is written primarily for agencies that want to develop an ICE process.
xvi ⢠Chapter 3, Typical ICE Process, provides a recommended, or âtypical,â ICE process based on lessons learned from existing state DOT processes. Agencies wanting to develop an ICE process can choose to use this process as a starting point, but will need to flesh out agency-specific details (e.g., specifying agency-preferred analysis tools) and decide which evaluation factors will be included in the process. Chapter 3 provides details about the essential factors recommended to be included in any ICE process along with details about additional factors an agency can include based on its specific goals, objectives, and desired level of effort. Agencies can also choose to substitute any element of the typical process with their own process, following the guidance provided previously in Chapter 2. Chapter 3 is written both for agencies wanting to develop an ICE process and agencies seeking ideas to improve an existing ICE process. ⢠Chapter 4, Implementing ICE. Once a draft ICE process has been developed, Chapter 4 presents the steps involved in implementing the process within the agency. This chapter discusses testing and refining the draft process, developing an ICE policy to require the use of the process, conducting pre- implementation outreach to users of the process, rolling out ICE agencywide, and monitoring and refining the process following implementation. Chapter 4 is written primarily for agencies that want to develop an ICE process. ⢠Chapter 5, Analysis Methods and Tools, describes methods and tools that can be used to support the typical ICE process in Chapter 4. These tools can be used to analyze an intersection conceptâs effects on safety; traffic operations; right-of-way, utility, and environmental impacts; construction costs; life- cycle costs; and social equity; and to document decisions made during the ICE process. An Appendix, Overview of Intersection Form and Control Types, provides descriptions and illustrations of a broad range of potential intersection forms, including the control types applicable to each form, issues to be considered with respect to users of specific travel modes, and other benefits and challenges associated with each form. Many state DOT ICE guidance documents include similar overviews, and the material in this chapter can be incorporated by agencies when developing their own guidance documents The ICE process incorporates a number of existing methods and tools commonly used by transportation agencies to evaluate traffic operations, safety, and other factors. In addition, the project developed or enhanced the following spreadsheet-based tools, which are available on the National Academies Press website (nap.nationalacademies.org) by searching for NCHRP Research Report 1087: Guide for Intersection Control Evaluation, to help practitioners implement the projectâs new and enhanced ICE processes and methods: ⢠ICE Process Tool. This tool uses information about the intersecting roadways (e.g., functional class, number of lanes, daily traffic, available right-of-way) and the intersectionâs context to recommend an initial list of intersection forms to study. The tool also provides templates for documenting the analysis results and decisions made during the ICE process. ⢠Capacity Analysis for Planning of Junctions (CAP-X) Tool. This is an updated version of FHWAâs CAP-X tool for estimating an intersectionâs volume-to-capacity ratio. The updated tool incorporates this projectâs recommended planning-level pedestrian and bicyclist safety assessment method. ⢠Planning and Preliminary Engineering Applications Guide Tool for Intersection Control Evaluation (PPEAG ICE Tool). This spreadsheet adds the planning-level traffic operations analysis methods developed by this project for innovative intersection forms to the methods for conventional intersection forms covered by NCHRP Report 825: Planning and Preliminary Engineering Applications Guide to the Highway Capacity Manual (Dowling et al. 2016) and its accompanying spreadsheet tools. ⢠Equity Assessment Tool. This spreadsheet provides templates for documenting the results of the projectâs recommended social equity evaluation process.
xvii ⢠Design Flag Calculator Tool. This tool provides templates for documenting the results of the â20 design flagsâ method for assessing pedestrian and bicyclist comfort and safety at an intersection, applying the method described in NCHRP Research Report 948: Guide for Pedestrian and Bicyclist Safety at Alternative and Other Intersections and Interchanges (Kittelson & Associates, Inc., et al. 2020). ⢠SSI Score Calculator ToolâIntersection and SSI Score Calculator ToolâInterchange. These tools implement the SSI analytical method developed by Porter et al. (2021) for FHWA. These versions of the tools modify the original method to only address motor vehicle safety at a planning- level. The projectâs recommended planning-level methods for evaluating pedestrian and bicyclist safety are incorporated into the updated CAP-X tool described above. ⢠Safety Performance for Intersection Control Evaluation (SPICE). This toolâs methodology is identical to FHWAâs SPICE Tool Version 1.4, but the spreadsheet has been modified to include overview and instructions sheets consistent with the other NCHRP Project 17-98 tools. ⢠Life-Cycle Cost-Estimating Tool (LCCET). This tool updates the LCCET developed by NCHRP Project 03-110 (Rodergerdts et al. 2016) by replacing state-specific unit costs with national default values. Analysts can override these default values as needed with local values. Conclusions The state DOTs that have adopted formal ICE processes have found them to be successful at achieving a variety of DOT objectives, including considering alternatives to conventional signalized intersections (e.g., roundabouts, innovative intersections), providing decision-making consistency and defensibility, and incorporating context- and performance-based approaches to decision-making. However, these outcomes do not take place overnight; it took eight to ten years for the early adoptersâ ICE policies to really take root within the organizations and achieve full adoption. All of the early adopters reported that their roadway designers have broken out of the âtraffic signal firstâ mentality. ICEâs ability to incorporate multiple evaluation factorsâsome quantitative and others qualitativeâhelps ensure that a variety of potential benefits and challenges arising from an intersection concept are identified, evaluated, and used to arrive at a decision on a preferred concept. This ability, when combined with the documentation processes built into an ICE process, leads to a more transparent and defensible decision- making process. Although ICE may increase the up-front analysis work when developing an intersection project, it also minimizes the risk that unexpected obstacles will arise during design and construction that create delays or added costs, or that unintended issues will arise after opening that require costly mitigation and potentially harm the agencyâs reputation. In addition, ICE processes typically are designed to be flexible, balancing analysis needs against project scale and context. A well-designed ICE process allows the process to end early if only one viable configuration remains. In a successful ICE process, planning-level and qualitative evaluation methods are used to quickly filter out infeasible intersection configurations, while reserving more detailed analysis efforts to identify the best-performing option out of the configurations that remain. Factors that help facilitate the adoption of ICE processes within an agency include: ⢠Training and educationâboth among agency staff and among consultants who might be called upon to perform ICE analysesâare of paramount importance for achieving agencywide adoption and consistent results. ⢠Codifying ICE policy and integrating it in a consistent fashion into the design process is one of the largest predictors of success. ⢠Implementing ICE policy early in the project (during scoping) seems to avoid issues down the line â in cost, design time, and public acceptance.
xviii ⢠FHWA support and encouragement of states to develop ICE policies has been important, based on responses from states currently in the process and those that that had previously adopted ICE policies. This projectâs work has advanced the state of the practice for performing ICE through: ⢠Recommending a process for developing and implementing ICE within an agency, based on success stories and best practices from early adopters. ⢠Developing guidance for conducting an ICE process, based on the experience of early adopters, combined with additional case study testing. ⢠Addressing gaps in current evaluation tools to (1) allow a broader range of intersection configurations to be consistently analyzed and (2) facilitate quick, reasonably accurate, planning-level analyses for a greater variety of evaluation factors. ⢠Developing a social equity analysis method that forces analysts and agencies to step back from CADD drawings and software analysis output to consider the intersectionâs multiple roles in serving users, not just those in motor vehicles, and how the intersection should be designed to match the context of the community in which it is located.
