Minnesota Department of Transportation

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Research & Innovation

Speed Impacts from Roundabouts and Other Traffic Control Devices

Need Statement 718


Based on the recent LRRB report “Strategies for Effective Roundabout Speed Reduction” and past literature, roadway geometry and intersection traffic control are typically some of the best tools that roadway design engineers actually have to influence vehicular speed. Roundabouts have shown to be exceptional at lowering operating speed and providing traffic calming to various roadways. However, the exact impacts and expected operating speeds of vehicles entering and exiting roundabouts and various intersections is not well known with specific speed information. This study would build on the mentioned LRRB report and seek to understand the speed which drivers use to enter and exit roundabouts, signals, and other various traffic control types. Data collection would include speed collection at:

  • 1,000 feet before RABT
  • Entering RABT
  • Leaving RABT
  • 1,000 feet after RABT


This could be helpful during intersection control evaluation reports, geometric design, and with public engagement. Better understanding of speed and speed selection could help to build on through-put capacity and safety consequences of the various intersection controls as well. This research could explore geometric features for how they influence overall speed upon approach. These could then be better understood, added to existing manuals, and result in better speed management and control for intersection approaches.

Additional research could be provided to better understand capacity and delay at existing single lane roundabouts to build on the capacity limits of single lane roundabouts.

Roundabouts are typically challenged by the public due to numerous factors. This research and data could help answer questions regarding speed and roundabouts effectiveness of speed reduction.

Strategic priorities

  • Safety: Roundabouts are a proven safety countermeasure per the FHWA. Public resistance is common as roundabouts are not understood, and people often do not understand why roundabouts work. A better understanding of the speed profiles of vehicles approaching the roundabout versus other traffic control types could help highlight why roundabouts are effective. This could lead to better engagement with the public and more roundabouts being installed.

Expected outcomes

  • New or improved technical standard, plan, or specification
  • New or improved manual, handbook, guidelines, or training
  • New or improved tool or equipment

Technical advisory panel

Suggested members for the TAP:

  • Doug Carter, MnDOT GDSU.
  • Morrie Luke, MnDOT D1.
  • Ken Johnson, MnDOT OTE.
  • Sonja Piper, MnDOT OTE
  • Hannah Pritchard, MnDOT OTAT
  • Joe Gustafson, Washington County
  • Luis Flores, Ramsey County
  • Chad Hausmann, Wright County
  • Tim Plath, Eagan
  • Ross Beckwith, West Saint Paul