The National Academies

NCHRP 03-60 [Completed]

Capacity and Quality of Service of Interchange Ramp Terminals

  Project Data
Funds: $299,904
Research Agency: Pennsylvania State University
Effective Date: 5/30/2001
Completion Date: 12/30/2004
Comments: Results incorporated into the HCM

Objective: The objectives of this project were to develop improved methods for capacity and quality-of-service analysis of interchange ramp terminals and nearby intersections and to recommend a revised Chapter 26 of the Year 2000 Highway Capacity Manual that addresses a full range of interchange types. The chapter should indicate when simulation should be considered in lieu of analytical methods.

Status: The research results have been published as a stand-alone chapter of the HCM and they will be incorporated into the
2010 edition of the HCMNCHRP Project 03-60A is conducting further validation tests of the methodology.

Background: Chapter 26, "Interchange Ramp Terminals," of the Year 2000 Highway Capacity Manual (HCM) includes general material for analyzing interchange ramp terminals. Although the chapter presents ideas and concepts relating to most types of interchanges that include two intersections, it focuses primarily on signalized, two-intersection diamond interchanges and single-point urban interchanges. Since a complete methodology for predicting the impact of the interaction between the two intersections is not available, the chapter is primarily conceptual in content.

Tasks: Accomplishment of the project objectives will require at least the following tasks. (1) Analyze, describe, and critique pertinent domestic and international literature to identify suitable concepts for defining the quality of service of an interchange ramp terminal area. Identify and critically review existing tools suitable for planning, design, and operational analysis of interchange types, ramp terminals, nearby intersections, and traffic control. Particular attention should be paid to the final report of NCHRP Project 3-47, Capacity Analysis of Interchange Ramp Terminals. (2) Identify and categorize interchange types on the basis of how their operation would be analyzed. For each category, identify the critical movements, geometric elements, traffic control elements, and how they affect each other. This effort should consider operation on the exit and entrance ramps but not on the freeway proper. (3) Develop a concept for expressing the quality of service of interchange ramp terminal systems. The concept should allow the operation of different interchange types and traffic control schemes to be compared, considering nearby intersections if their operation interacts with the interchange ramp terminals. Define appropriate performance measures for critical movements and the overall system of interacting intersections. The performance of the freeway ramps and the surface street and their impact on each other must be considered. Consideration should be given to which performance measures are most appropriate for planning, design, and operational analyses and the quality of service concepts used in the HCM 2000. (4) Within 8 months of the contract start date, submit an interim report on the information developed in Tasks 1 through 3. The interim report shall also contain a detailed, updated work plan and a revised budget for the remaining tasks. (5) Assess existing analysis tools, including simulation and analytical methods, to determine their applicability for planning and design analysis. Select or develop and recommend an analytical procedure for planning and design analysis for inclusion in the HCM. The planning and design procedure should facilitate comparison of different interchange types and evaluation of geometric design details for the ramp terminals and surface street. The planning and design procedure should not require detailed signal timing data. It may include checklists, service volume tables, and critical lane volume analysis. (6) Using field data, assess existing analysis tools, including simulation and analytical methods, to determine their applicability for operational analysis. An operational analysis should address the full range of traffic control schemes (i.e., actuated and fixed-time traffic signals, stop and yield control) and consider the impact of nearby intersections, exit ramp queuing, and entrance ramp metering on the performance measures. The impact of the freeway ramps and surface street operation on each other should be assessed, as should oversaturated conditions. Modification of existing tools is not anticipated. Define functional requirements for simulation models suitable for interchange ramp terminal areas. (7) Apply the planning and design procedure and the best operational analysis tool(s) to example problems representing the various interchange types. Show how operational analysis tools can be used in conjunction with the planning and design procedure during the design of an interchange. (8) Rewrite Chapter 26 and its appendices to address a full range of interchange types. The chapter should include a comprehensive quality-of-service approach, a complete presentation of the planning and design procedure, a strategy for using operational analysis tools, and appropriate example problems from Task 7. (9) Submit a final report that documents the entire research effort and includes the Task 8 chapter as a stand-alone document. The report should describe any impact on other chapters of the HCM and identify any needed improvements to existing analysis tools that were assessed during the course of the research.

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