A roundabout is a type of circular intersection, but is quite unlike a neighborhood traffic circle or large rotary. Roundabouts have been proven safer and more efficient than other types of circular intersections.
Roundabouts have certain distinguishing features and characteristics (as shown in the adjacent diagram). While these noted features are common to many roundabouts, they are not always present, as roundabouts are adapted to the context of the location. In fact, roundabouts don't even need to be perfectly circular! Successful roundabouts come in all shapes and sizes. Some are oval-, teardrop-, peanut- and dogbone- shaped. Some have as few as three legs and others as many as six. There are small, simple mini roundabouts, and larger, more complex multilane roundabouts. However, regardless of size, circular shape, or number of legs, the fundamental and essential characteristics of all roundabouts include:
Counterclockwise Flow. Traffic travels counterclockwise around a center island. Entry Yield Control. Vehicles entering the roundabout yield to traffic already circulating. Low Speed. Curvature that results in lower vehicle speeds, generally 15-25 MPH, throughout the roundabout.
Roundabouts can provide lasting benefits and value in many ways. They are often safer, more efficient, less costly and more aesthetically appealing than conventional intersection designs. Furthermore, roundabouts are an excellent choice to complement other transportation objectives – including Complete Streets, multimodal networks, and corridor access management – without compromising the ability to keep people and freight moving through our towns, cities and regions, and across the Nation. The FHWA Office of Safety identified roundabouts as a Proven Safety Countermeasure because of their ability to substantially reduce the types of crashes that result in injury or loss of life. Roundabouts are designed to improve safety for all users, including pedestrians and bicycles.
Most significantly, roundabouts REDUCE the types of crashes where people are seriously hurt or killed by 78-82% when compared to conventional stop-controlled and signalized intersections, per the AASHTO Highway Safety Manual.
By reducing the number and severity of conflict points, and because of the lower speeds of vehicles moving through the intersection, roundabouts are a significantly safer type of intersection. The diagram below excerpted from Roundabouts: An Informational Guide, Second Edition (published as NCHRP Report 672) illustrates the difference in conflict points between a conventional, four-legged intersection and an equivalent single lane roundabout. There are 32 conflict points associated with a conventional intersection – 8 merging (or joining), 8 diverging (or separating) and 16 crossing. In contrast, there are only 8 total conflict points at an equivalent roundabout – 4 merging and 4 diverging. Not only are conflict points halved with the roundabout, the type of conflicts that remain are the same-direction variety, which result in substantially less severity, and as a result, less likelihood of injury. The reduction of both the total number of conflict points and their severity is also true for pedestrians, also shown below in diagrams excerpted from the Guide.
Like any new technology or idea, it is necessary that people understand how roundabouts work and why they are needed. This conversation begins by communicating the magnitude and importance of the intersection safety challenge. With roughly ¼ of all traffic fatalities in the United States associated with intersections, it is critical that safer designs are implemented as widely and routinely as possible. But safer designs must also keep people and goods moving. Roundabouts have proven to be a safer and more efficient type of intersection. Still, because they may be unfamiliar to most people, successful implementation of a roundabout requires extra outreach and education. To help state and local road agencies advance roundabouts, the FHWA produces materials intended to communicate the advantages and benefits of roundabouts to a variety of different audiences. Many of these resources can be found in the Roundabouts Outreach & Education Toolbox, and are also listed below:
Information Videos Modern Roundabouts: A Safer Choice [YouTube] [WMV] [MOV] – Script Text [HTML] [PDF]
Modern Roundabouts: An Innovative Solution to Intersection Safety Concerns [YouTube] Informational Brochures Modern Roundabouts: A Safer Choice [HTML] [PDF (English)] [PDF (Spanish)]
Roundabouts with Pedestrians & Bicycles – A Safe Choice for Everyone [HTML] [PDF]
Roundabouts and First Responders – Saving Lives Together [HTML] [PDF]
Roundabouts along Rural Highways [HTML] [PDF]
Roundabouts and Tribal Governments [HTML] [PDF] Intersection Safety Case Study Series Minnesota Roundabout – A Scott County Success Story [HTML] [PDF] [PPT]
Roundabouts – The Maryland Experience: A Maryland Success Story [HTML] [PDF] [PPT] Roundabouts Outreach & Education Toolbox [HTML] Washington County MN Educates Drivers Through "Roundabout U" [HTML] [PDF]
Carmel IN Engages the Public Through Print and Web Outreach [HTML] [PDF]
Washington State Focuses on Outreach, Illustrates How to Drive a Roundabout [HTML] [PDF]
Bend OR Teaches Through Children Using Coloring Books to Communicate About Roundabouts [HTML] [PDF]
Missouri DOT Convinces Skeptics That Roundabouts Work [HTML] [PDF]
Iowa DOT Provides "Expert-on-Hand" Technical Assistance to Promote Roundabouts [HTML] [PDF]
Virginia DOT's Roundabouts Review Committee Spearheads Outreach Efforts [HTML] [PDF]
Brown County WI Roundabouts Calm Traffic, Improve School Zone Safety [HTML] [PDF]
Clearwater FL Public Charrettes Produce Strong Support for Roundabouts [HTML] [PDF]
Sioux Falls SD Conducts Roundabout Rodeo [HTML] [PDF]
Washington State DOT Hosts Roundabout Rodeo [HTML] [PDF]
Montpelier VT Constructs Roundabout with Local Roundabouts Steering Committee [HTML] [PDF]
Madison WI Makes Roundabouts Work for Pedestrians and Bicycles [HTML] [PDF]
Wisconsin DOT Engages Freight Stakeholders in the Roundabout Design Process [HTML] [PDF]
Santa Cruz CA Chooses a Roundabout as a Multimodal Solution [HTML] [PDF]
Austin TX Hosting General Information Briefings to Promote Roundabouts [HTML] [PDF]
Kansas DOT Designing Roundabouts for Truck Traffic [HTML] [PDF] Other Pedestrian and Bicycle Case Studies and Educational References Pedestrian and Bicycle Information Center (PBIC) Roundabouts General Information [HTML] Roundabouts FAQ [HTML]
PEDSAFE Pedestrian Safety Guide and Countermeasure Selection System Roundabouts General Information [HTML] Fort Pierce FL Case Study [HTML] Montpelier VT Case Study [HTML] Green Bay WI Metropolitan Area Case Study [HTML] Village of Great Neck Plaza, NY Case Study [HTML]
BIKESAFE Bicycle Safety Guide and Countermeasure Selection System Roundabouts General Information [HTML] University Place WA Case Study [HTML]
Safe Routes to School (SRTS) Clearinghouse Roundabouts General Information [HTML] Bellevue WA Case Study [PDF]
Public Roads Magazine Articles "Roundabouts Coming Full Circle", Vol. 81 No. 3 [HTML]
"They're Small But Powerful" (Mini Roundabouts), Nov/Dec 2012, Vol. 76, No. 3 [HTML]
"Bicyclist- and Pedestrian-Only Roundabouts", Jan/Feb 2009, Vol. 72, No. 4 [HTML]
"Does Your Interchange Design Have You Going Around in Circles?", Nov/Dec 2002, Vol. 66, No. 3 [HTML]
"Roundabout Safety Comes to America", Autumn 1995, Vol. 59, No. 2 [HTML]
Roundabouts: An Informational Guide, Second Edition (published as NCHRP Report 672) (TRB/FHWA 2010) [PDF]
Roundabouts: An Informational Guide, First Edition (FHWA, 2000) SUPERCEDED [PDF]
Roundabouts Technical Summary (FHWA, 2009) [HTML] [PDF] [PPT]
Mini Roundabouts Technical Summary (FHWA, 2009) [HTML] [PDF] [PPT]
Safety Aspects of Roundabouts (Short Version) (FHWA, 2007) [HTML] [PDF] [PPT]
Safety Aspects of Roundabouts (Long Version) (FHWA, 2007) [HTML] [PDF] [PPT]
Manual on Uniform Traffic Control Devices (FHWA, 2009)
Full Document [HTML] [PDF] – Part 2 Signing [HTML] – Part 3 Markings [HTML]
Temporary Traffic Control for Building & Maintaining Single & Multilane Roundabouts (ATSSA/FHWA, 2012) [HTML] [PDF]
An Evaluation of Signing for Three-Lane Roundabouts (FHWA, 2010) [HTML] [PDF]
Roundabouts and the ADA Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities - A Guidebook (NCHRP Report 834) (2016) [HTML]
Study of the Effect of ADA Accessibility on Kansas Roundabouts (Kansas, 2008) [HTML]
Information from FHWA on Accessible Planning, Design and Construction in the Public Right-of-Way [HTML]
Proposed Accessibility Guidelines for Pedestrian Facilities in the Public Right-of-Way (also known as PROWAG) NPRM Version (USAB, 2011) [HTML] [PDF]
Crossing Solutions at Roundabouts and Channelized Turn Lanes for Pedestrians with Vision Disabilities (published as NCHRP Report 674) (TRB, 2011) [PDF] – Supporting Material and Report Appendices [PDF]
Road Commission for Oakland County (Michigan) Pedestrian Hybrid Beacon and Rectangular Rapid Flash Beacon Study – Final Report (RCOC, 2011) [PDF]
Synthesis of Literature Relevant to Roundabout Signalization to Provide Pedestrian Access (USAB, 2007) [HTML] [PDF]
Pedestrian Access to Roundabouts: Assessment of Motorists' Yielding to Visually Impaired Pedestrians and Potential Treatments to Improve Access (FHWA, 2006) [HTML] [PDF]
Pedestrian Access to Modern Roundabouts: Design and Operational Issues for Pedestrians who are Blind (USAB, 2002) [HTML]
National Highway Institute Course #380096 "Modern Roundabouts: Intersections Designed for Safety" [HTML] [PDF]
Transportation Research Board Roundabouts Conference Proceedings (via TeachAmerica) [2005] [2008] [2011] [2014] [2017]
Proceedings from Northeast U.S. Roundabouts Peer Exchange (2010) [Materials] [Recordings]
State Highway Agency Roundabouts Resources (click on orange-shaded boxes to open link in browser):
Evaluation of Safety and Mobility of Two-Lane Roundabouts (Minnesota, 2017) [PDF]
Strategies for Effective Roundabout Approach Speed Reduction (Minnesota, 2017) [PDF]
Roundabout Practices (NCHRP Synthesis 488) (2016) [PDF]
Estimating the Life-Cycle Cost of Intersection Designs (NCHRP Web-Only Document 220) (2016) [PDF] and Tool [XLS]
Evaluation of Heavy Vehicles on Capacity Analysis for Roundabout Design (Nextrans, 2016) [PDF]
Roundabout Design Training for Alaska's Engineers (PacTrans, 2015) [PDF]
Evaluation of Alternative Intersections and Interchanges Volume I - Roundabout Capacity and Rollover Analysis for Heavy Vehicles (Indiana, 2015) [PDF]
Evaluating the Performance of Corridors with Roundabouts (NCHRP Report 772) (2014) [PDF]
Accelerating Roundabout Implementation in the United States (Seven Volume Series) (FHWA, 2015)
Volume I – Evaluation of Rectangular Rapid-Flashing Beacons (RRFB) at Multilane Roundabouts – Final Report [PDF]
Volume II – Assessment of Roundabout Capacity Models for the Highway Capacity Manual – Final Report [PDF]
Volume III – Assessment of the Environmental Characteristics of Roundabouts – Final Report [PDF]
Volume IV – Review of Fatal and Severe Injury Crashes at Roundabouts – Final Report [PDF]
Volume V – Evaluation of Geometric Parameters that Affect Truck Maneuvering and Stability – Final Report [PDF]
Volume VI – Investigation of Crosswalk Design and Driver Behaviors – Final Report [PDF]
Volume VII – Human Factor Assessment of Traffic Control Device Effectiveness – Final Report [PDF]
Evaluating the Performance of Corridors with Roundabouts (published as NCHRP Report 772) (2014) Report [PDF] – Appendices B-J [PDF] – Appendix K [PDF] – Appendices L-O [PDF] – Overview Presentation [PPT]
Kansas Roundabout Guide, Second Edition (A Companion to NCHRP Report 672) (Kansas, 2014) [PDF]
Implementation, Driver Behavior and Simulation: Issues Related to Roundabouts in Northern New England (Vermont, 2014) [PDF]
Roundabouts and Access Management (Florida, 2014) [PDF]
Effect of Signing and Lane Markings on the Safety of a Two-Lane Roundabout (Minnesota, 2014) [PDF]
Information/Education Synthesis on Roundabouts (Montana, 2013) [PDF]
Best Practices for Roundabouts on State Highways (Indiana, 2013) [PDF]
Wisconsin Roundabout Guide (Wisconsin, 2013) [PDF]
Statewide Roundabout Operations Monitoring and Evaluation (Wisconsin, 2013) [HTML]
Developing Safety Performance Measures for Roundabout Applications in the State of Oregon (Oregon, 2013) [PDF]
Accommodating Oversize/Overweight (OSOW) Vehicles at Roundabouts (Kansas, 2013) [PDF]
Investigation of Pedestrian/Bicycle Risk in Minnesota Roundabout Crossings (Minnesota, 2012) [PDF]
Demonstration of Roundabout Lighting Based on the Ecoluminance Approach (New York, 2012) [PDF]
Joint Roundabout Truck Study (Minnesota/Wisconsin, 2012) [PDF]
A Study of the Impact of Roundabouts on Traffic Flows and Business (Kansas, 2012) [PDF]
Texas Roundabout Guidelines (Texas, 2011) [PDF]
Evaluating the Performance and Safety Effectiveness of Roundabouts (Michigan, 2011) [PDF]
Improving Drivers' Ability to Safely and Effectively Use Roundabouts: Educating the Public to Negotiate Roundabouts Final Report (Michigan, 2011) [PDF]
Roundabouts in the United States (published as NCHRP Report 572) (2007) Report [PDF] – Appendices [PDF]
Lane Restriction Signing and Markings for Double Lane Roundabouts (Multistate Pooled Fund Study, 2007) [PDF]
Operational Performance of Kansas Roundabouts (Kansas, 2004) [PDF]
Modern Roundabout Practice in the United States (published as NCHRP Synthesis 264) (1998) [PDF]
Biteme178938281 on February 1st, 2020 at 22:55 UTC »
Now if people actually knew how to use them, it would make using them more pleasurable. But, we have them all over and no one uses them right.
TheSanityInspector on February 1st, 2020 at 22:50 UTC »
Some 4-way stops in my area were changed to roundabouts, and the improvement was remarkable.
PhilMac555 on February 1st, 2020 at 22:26 UTC »
Come to Ireland and those stats are out the window. We put traffic lights on ours which brings everything to a standstill