Determining Guidelines for Ramp and Interchange Spacing (2011) / Chapter Skim
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Chapter 1 Introduction
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NCHRP 3-88 Final Report Guidelines for Ramp and Interchange Spacing Chapter 1: Introduction 1-1 Chapter 1 INTRODUCTION The purpose of NCHRP Project 3-88 was to investigate the impact of ramp and interchange spacing on traffic operations and safety and to develop a set of guidelines to help users consider ramp and interchange spacing needs when planning and assessing new or reconstructed freeway facilities. The project team used simulation models, calibrated with field data, to assess the impact of ramp spacing on freeway speed.
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Final Report NCHRP 3-88 Chapter 1: Introduction Guidelines for Ramp and Interchange Spacing 1-2 experience from the project's panel was accessed. Information gathering activities are fully discussed in Chapter 2 of this report.
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NCHRP 3-88 Final Report Guidelines for Ramp and Interchange Spacing Chapter 1: Introduction 1-3 o Project 3-37: Capacity of Ramp-Freeway Junctions o Project 3-75: Analysis of Freeway Weaving Sections o Project 3-92: Production of the 2010 Highway Capacity Manual • Reviewing the HCM to identify any minimum ramp or interchange spacing values or other thresholds dictated by traffic operations considerations. • Collecting field data and conducting simulation modelling The project team's review of data from previous NCHRP projects revealed little about the impact of ramp spacing or interchange spacing on mainline freeway speed.
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Final Report NCHRP 3-88 Chapter 1: Introduction Guidelines for Ramp and Interchange Spacing 1-4 indicated that ramp spacing has an impact on mainline freeway speeds except at moderate to high (1500+ vphpl) mainline volume.
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NCHRP 3-88 Final Report Guidelines for Ramp and Interchange Spacing Chapter 1: Introduction 1-5 • Chapter 2 presents relevant federal, state, and local policies. • Chapter 3 discusses elements of geometric design and freeway signing relevant to ramp and interchange spacing • Chapter 4 discusses traffic operations and safety considerations for ramp and interchange spacing • Chapter 5 presents ranges of recommended ramp and interchange spacing dimensions • Chapter 6 presents five scenario-based case studies that apply the principles presented in the preceding chapters • The Appendix presents tools and findings developed as part of the operations work plan 1.3.4 Resource Document Revisions Based upon the findings of this project, the project team revisited relevant sections of the AASHTO Green Book, HCM, MUTCD, and HSM to determine if changes should be made.
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