OBJECTIVE
The objective of this project was to enhance the analysis methods outlined in the new Chapter 26 of the HCM. This enhancement was accomplished by validating the basic methodology and extending the methodology to handle interchanges with roundabouts at the ramp terminals and include the impacts of adjacent signalized intersections.
STATUS
Field data was collected at seven sites and the methodology evaluated against it. A revised chapter was delivered in July 2009 for review by the NCHRP panel and the TRB Committee on Highway Capacity and Quality of Service Committee. The chapter was revised and included in the Year 2010 edition of the Highway Capacity Manual.
BACKGROUND
NCHRP Project 3-60, "Capacity and Quality of Service of Interchange Ramp Terminals," developed improved methods for capacity and quality-of-service analysis of interchange ramp terminals and recommended a revised Chapter 26 of the Highway Capacity Manual (HCM) that addresses a full range of interchange types. The chapter has been delivered to the TRB Committee on Highway Capacity and Quality of Service. It has been released as a stand-alone chapter and is intended to be included in the Year 2010 edition of the HCM (see NCHRP Project 3-92, "Production of the Year 2010 Highway Capacity Manual").
The methodology was based primarily on the results of microscopic simulation because the budget allowed only limited field data collection. This approach has caused concerns with the robustness of the procedure. Additional research is needed to validate the basic methodology and to extend the methodology to allow analysis of a broader range of interchange designs.
TASKS
Task 1. Describe the critical data needs for validating and improving the existing Chapter 26 methodology and those needed for adding adjacent signalized intersections. Develop a data collection plan that balances the needs to (1) validate the existing methodology, (2) improve the robustness of the methodology, and (3) extend the methodology to handle adjacent signalized intersections.
Task 2. Meet with the project oversight panel to refine the data collection plan.
Task 3. Carry out the data collection plan as approved by the panel.
Task 4. Analyze the data and develop recommended enhancements to the HCM Chapter 26 methodology (including the effects of adjacent signalized intersections).
Task 5. Use the results of NCHRP Report 572: Roundabouts in the United States and other relevant efforts to extend the procedure to handle interchanges with roundabouts at the ramp terminals.
Task 6. Prepare a revised draft Chapter 26 and present it to the TRB HCQS Committee at their January 2009 meeting. The chapter should facilitate comparison of different interchange configurations. The chapter should be submitted in the format of the most current version of the Microsoft Office Suite that is in widespread use in the user community. Revise the draft chapter considering the comments from the NCHRP project panel and the TRB HCQS Committee.
Task 7. Submit a final report documenting the entire research effort and submit the draft HCM Chapter 26 using customary U.S. units with text, graphics, and sample problems in electronic format.
