An Updated Capacity Model for Mini-Roundabouts

Mini-roundabouts, characterized by their fully traversable central islands, provide a compact and efficient alternative to traditional single-lane roundabouts. They are particularly beneficial in areas with spatial constraints, where larger roundabouts would necessitate unwanted right-of-way impacts. The typical inscribed circle diameter (ICD) of these mini-roundabouts is often under 90 feet, and they are best suited for areas where speeds are limited to 30 mph or lower. One of the primary advantages of mini-roundabouts is their smaller footprint, making them an effective replacement for stop signs or signal controls at intersections with moderate traffic volumes. Their traversable central island design is pivotal, offering adaptability in mixed traffic scenarios, especially facilitating the movement of larger vehicles. However, there are aspects that require further scrutiny. In the early 2010s, the Federal Highway Administration (FHWA) developed capacity models for mini-roundabouts with two different ICDs. These models assumed that such roundabouts would function as a series of independent T-intersections, an assumption that may not always be accurate, especially in the presence of larger vehicles. When comparing the capacities of mini-roundabouts with all-way stop-controlled (AWSC) intersections, it is vital to understand their potential advantages and shortcomings. If mini-roundabouts do not significantly exceed the capacity of AWSC intersections, their unique positioning in traffic management might be challenged, especially when considering the cost-effectiveness of AWSC intersections. The main objective of this research is to develop new capacity models for mini-roundabouts based on field data collected at 25 mini-roundabouts in North Carolina and other states within the midatantic and southeast regions. Video data will be recorded at all sites from 25-30 ft elevation. The videos will be analyzed using the DataFromSky (DFS) service, which the team successfully utilized in previous NCDOT projects. Vehicle trajectories will be obtained and analyzed to estimate key capacity parameters, including the critical and follow-up headways and the effect of heavy vehicles. The team will utilize a calibrated microsimulation model only to fill out gaps when field data are not available.

Language

• English

Project

• Status: Active
• Funding: $247743
• Contract Numbers:

  RP2025-05

• Sponsor Organizations:

  North Carolina Department of Transportation

  Research and Development
  1549 Mail Service Center
  Raleigh, NC  United States  27699-1549
• Managing Organizations:

  North Carolina Department of Transportation

  Research and Development
  1549 Mail Service Center
  Raleigh, NC  United States  27699-1549
• Project Managers:

  Bryant, Catherine

• Performing Organizations:

  North Carolina State University, Raleigh

  Department of Civil Engineering, Campus Box 7908
  Raleigh, NC  United States  27695-7908
• Principal Investigators:

  Hajbabaie, Ali

• Start Date: 20240716
• Expected Completion Date: 20260715
• Actual Completion Date: 0

Subject/Index Terms

• TRT Terms: Diameter; Headways; Highway capacity; Highway design; Microsimulation; Traffic data; Vehicle trajectories; Video
• Subject Areas: Design; Highways; Operations and Traffic Management; Planning and Forecasting;

Filing Info

• Accession Number: 01937048
• Record Type: Research project
• Source Agency: North Carolina Department of Transportation
• Contract Numbers: RP2025-05
• Files: RIP, STATEDOT
• Created Date: Nov 15 2024 4:06PM