Impact of S-Curves on Speed in a Modern Roundabout

According to the United States Department of Transportation (USDOT), around 20 people per day die at signalized intersections, with most of these caused by angle or head-on crashes. The USDOT’s Federal Highway Administration (FHWA) has identified modern roundabouts to be substantially safer than signalized intersections, due in part to the reduction in conflict points from 32 for a traditional signalized intersection to 8 for a modern roundabout. Despite the increased adoption of modern roundabouts across the US, there are a number of specific design elements for which the direct impact they have on operational and safety-related performance of the roundabout remains unknown. To be specific, there is currently no conclusive research on the direct speed effects related to the introduction of a reverse curve (S-curve) and its geometric characteristics on the approach to a roundabout. This research employed a series of microsimulation-based analyses to investigate the speed-related impacts related to the introduction to S-curves on the entry of a roundabout. An existing roundabout in Amherst, MA, USA, was used as a case study for this experiment. The existing geometry was initially modeled, after which the conventional linear approach was modified to an S-curve and evaluated. Field data from the locations were used to calibrate microsimulation models developed in AIMSUN. The resulting trajectory data was analyzed for both the base case as well as three levels of experimental S-curves (ranging from 30 to 60 degrees) on each roundabout approach (16 total). The results provide evidence to suggest that a significant reduction in speed can be realized with a minimal amount of reverse curvature on the roundabout approach.

• Record URL:
  http://safersim.nads-sc.uiowa.edu/final_reports/UM 3 Y1_Report.pdf
• 
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/35561
• Supplemental Notes:
  • This document was sponsored by the U.S. Department of Transportation, University Transportation Centers Program.
• Corporate Authors:

  Safety Research Using Simulation University Transportation Center (SaferSim)

  University of Iowa
  Iowa City, IA  United States  52242

  Office of the Assistant Secretary for Research and Technology

  University Transportation Centers Program
  Department of Transportation
  Washington, DC  United States  20590
• Authors:
  • Christofa, Eleni
  • Knodler Jr, Michael
  • Sabhanayagam, Akshaey
  • Hajiseyedjavadi, Foroogh
  • Khalighi, Farnoush
  • Campbell, Nicholas
• Publication Date: 2018-1

Language

• English

Media Info

• Media Type: Web
• Features: Figures; References; Tables;
• Pagination: 20p

Subject/Index Terms

• TRT Terms: Highway curves; Roundabouts; Traffic safety; Traffic speed; Trajectory
• Identifier Terms: AIMSUN (Computer model)
• Uncontrolled Terms: S curves
• Geographic Terms: Amherst (Massachusetts)
• Subject Areas: Highways; Operations and Traffic Management; Safety and Human Factors;

Filing Info

• Accession Number: 01667443
• Record Type: Publication
• Files: UTC, NTL, TRIS, ATRI, USDOT
• Created Date: Apr 26 2018 9:15AM