Modern Roundabouts – The Safer Intersection Choice Mark Doctor, PE - PowerPoint PPT Presentation

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Modern Roundabouts – The Safer Intersection Choice Mark Doctor, PE

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  1. Photo: Mt. Horeb, WI Proven Safety Measures Workshop January 10, 2010 Modern Roundabouts – The Safer Intersection Choice Mark Doctor, PE FHWA Resource Center Safety & Design Technical Service Team

  2. Presentation Overview • What is a modern roundabout? • (i.e., how is it different from other types of circular intersections?) • Why are roundabouts safer? • Where are roundabouts appropriate? • Where can I get more information?

  3. Counter-clockwise Circulatory Roadway Central Island Splitter Island Deflected Entry Path with Yield control Pedestrian Crossing What is a Modern Roundabout?

  4. Modern roundabouts are different from the older “Rotary” style intersections!!! Typically, modern roundabouts are – • smaller than rotaries • designed for slower entry, circulating, and exit speeds • always follow a “yield-at-entry” traffic control principle • designed with a raised splitter island to slow and deflect traffic prior to entry • designed to facilitate safer pedestrian crossings • designed to follow a same lane entry/lane exit principle at multilane roundabouts • (NO LANE CHANGES in the circulatory roadway)

  5. Older “Rotary” Circles are not Roundabouts !!! Cony Rotary Augusta, ME

  6. Signalized Traffic Circles are not Roundabouts !!! Dupont Circle, Washington, DC Is Not a Roundabout

  7. Modern roundabouts are different from traffic calming circles!!! Examples of traffic calming circles – NOT ROUNDABOUTS

  8. Roundabouts are a type or subset of circular intersections Key Message: Not all circular intersections are roundabouts!!! Roundabouts All circularintersections Others Rotaries Neighborhoodtraffic circles

  9. Why are roundabouts safer? The laws of physics!!! Comparison of Vehicle Conflict Points • 32 conflict points • High-speed • High-angle • High-energy • 8 conflict points • Low-speed • Low-angle • Low-energy 75% fewer conflicts Slide Credit: Michael Wallwork, PE

  10. A Common Geometric Control at an Intersection: “Right-in / Right-out”

  11. Roundabouts Operate Very Similarly – All Movements are “Right In / Right Out”

  12. Roundabouts also reduce Vehicle - Pedestrian Conflicts 16 Conflicts 8 Conflicts

  13. That all sounds good in theory …. but what do the “numbers” show? The Insurance Institute for Highway Safety – U.S. Roundabout Safety Report • Before-after studies at 24 intersections • 39% overall decrease in crashes • 76% decrease in injury crashes • 89% decrease in fatal/incapacitating crashes • 75% reduction in traffic delays! NCHRP Report 572 – Roundabouts in the US • Before-after studies at 55 intersections • 35% overall decrease in crashes • 76% decrease in injury crashes • 81% decrease in fatal/incapacitating crashes for single lane urban roundabouts • 71% decrease in fatal/incapacitating crashes for single lane rural roundabouts Key Message:: Roundabouts are SAFER !!!

  14. Where are roundabouts appropriate? • New intersections • Replacement of all-way stops • Replacement of two-way stops when side street delay becomes excessive • Replacement of signalized intersections • Roundabouts can better accommodate highly unbalanced movements • 3-leg intersections with heavy left-turn volumes

  15. Where are roundabouts appropriate? • Intersections with a high-crash rate or a higher severity of crashes Roundabouts may be particularly advantageous at: Roundabouts improve safety by simplifying traffic movements, reducing potential conflict points, and reducing vehicle speeds

  16. Where are roundabouts appropriate? • Intersections with complex geometry, skew angles, or more than four approaches Roundabouts may be particularly advantageous at: After Before Albuquerque, NM – Central Ave. and 8th

  17. Where are roundabouts appropriate? • Rural intersections with high-speed approaches Roundabouts may be particularly advantageous at: Elongated splitter islands with successive reverse curvature can greatly improve safety at high speed approaches by alerting drivers to a changed traffic condition ahead.

  18. Where are roundabouts appropriate? Roundabouts may be particularly advantageous at: • Intersections with high U-turn movements Roundabouts facilitate the use of raised medians for access management along the roadway by making U-turn movements easier at the intersections.

  19. Where are roundabouts appropriate? • Transitions or “Gateways” from higher speed to lower speed areas • Where aesthetics are important Roundabouts may be particularly advantageous at: Roundabouts make for good transitions in speed change (including rural to urban transitions).

  20. Where are roundabouts appropriate? High School Roundabouts may be particularly advantageous at: • Intersections near schools Roundabouts control speeds Gaylord, MI

  21. Roundabouts Near Schools “It definitely has improved the flow of traffic and has not proved to be the safety concern that several parents feared.” - Jeri Mifflin, Principal, Bennett Woods Elementary School Okemos, MI

  22. So, why aren’t more agencies using roundabouts? Pick Your Favorite Excuse: • “The public will lynch us if we propose a roundabout.” • “I know how people drive in my town – they’ll never get used to a roundabout.” • “We’ll get sued because of all the crashes it will cause.”

  23. Roundabouts are often confused with other types of circular intersections ≠ • “we have had a lot of people not very happy about the idea of roundabouts, but after they are constructed, those fears mostly go away.” • Brian Walsh - Washington State DOT

  24. Driver Opinion Survey on Roundabouts 63 41 31 15 OPPOSE FAVOR Source: Insurance Institute for Highway Safety

  25. Sometimes it takes perseverance!!! Photo source: NYSDOT

  26. Where can I get more information? • FHWA brochure – available • FHWA Technical Summary on roundabout design – Soon • FHWA Technical Summary on mini-roundabouts – Soon • FHWA DVD aimed at decision makers – Spring 2010 • One-day NHI Training Course on Roundabouts - mid 2010 • Updated Roundabout Informational Guide from NCHRP – mid 2010 • Ongoing research studies (NCHRP and others) on roundabout pedestrian safety and treatments for sight-impaired pedestrians

  27. For more information …. www.safety.fhwa.dot.gov or contact: Mark Doctor, FHWA Resource Center (404) 562-3732 mark.doctor@dot.gov

  28. Questions ???