Development of U.S. Vehicle Capacity Models for Multilane and Turbo Roundabouts

Turbo roundabouts are designed to limit improper lane changing behavior within multilane circulatory roads by providing physical lane separation. Turbo roundabouts also feature more radial entries than conventional designs, which may affect vehicle entry paths, speeds, and gap acceptance. Originating in Europe, turbo roundabouts have been gradually adopted internationally. Although many state, local, and tribal transportation agencies are contemplating turbo roundabouts as potential alternatives for new or reconstructed intersections to improve safety and operations, to date only a few have been constructed in the United States. A key question in implementing turbo roundabouts in the United States is vehicle capacity, as drivers may approach, enter, and navigate these facilities differently from conventional roundabouts. A U.S.-based capacity model for turbo roundabouts does not currently exist, and European models are not directly transferable due to differences in driver behavior, vehicle characteristics, and design practices. In addition, the existing multilane roundabout capacity model in the Highway Capacity Manual (HCM), 7th edition, was developed over a decade ago and cannot account for key geometric factors that influence capacity and operations. In addition, changes in design practices and increased driver familiarity with roundabouts may have further affected the model’s accuracy since its development. Research is needed to support efforts by state departments of transportation (DOTs) to assess operational performance of multilane and turbo roundabouts. The objective of this research is to develop adaptable vehicle capacity models for multilane and turbo roundabouts to accurately estimate performance by considering key geometric factors such as entry and exit angles, inscribed circle diameters, and physical separation.

• Record URL:
  • http://apps.trb.org/cmsfeed/TRBNetProjectDisplay.asp?ProjectID=5844
• Supplemental Notes:
  • Contract to a Performing Organization has not yet been awarded.

Language

• English

Project

• Status: Proposed
• Funding: $600,000.00
• Contract Numbers:

  Project 07-38

• Sponsor Organizations:

  National Cooperative Highway Research Program

  Transportation Research Board
  500 Fifth Street, NW
  Washington, DC  United States  20001

  American Association of State Highway and Transportation Officials (AASHTO)

  444 North Capitol Street, NW
  Washington, DC  United States  20001

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Project Managers:

  Zhao, Yi

• Start Date: 20261001
• Expected Completion Date: 0
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Behavior; Drivers; Feasibility analysis; Geometric design; Highway capacity; Highway design; Roundabouts
• Geographic Terms: United States
• Subject Areas: Design; Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01956435
• Record Type: Research project
• Source Agency: Transportation Research Board
• Contract Numbers: Project 07-38
• Files: TRB, RIP
• Created Date: May 28 2025 9:52AM