Perhaps the best overall site on Roundabouts comes from the Maryland Department of Transportation’s State Highway Administration. The animation on the opening page is worth 10,000 words and hopefully will clearly illustrate that roundabouts are NOT traffic circles:

Maryland State Highway Administration

One of the biggest problem with roundabouts is the negative, initial public perception. However, that often changes after the roundabout is installed, a fact that is referenced in many of the documents below and reinforced in this editorial from a Maryland newspaper:

Roundabout Reversal

This 82 page report from the Transportation Research Board - National Research Council is must reading for anyone seriously studying roundabouts. It provides an in-depth look at roundabouts from a wide variety of perspectives and includes significant “before and after” data on such topics as safety, congestion relief, capacity, public acceptance and more:

National Cooperative Highway Research Program Roundabout Study (1.75 MB)

An in-depth look by Maryland’s Department of Transportation into the effectiveness of roundabouts in that state. Included is a variety of study data regarding safety, congestion relief and a very interesting cost/benefit analysis:

Maryland’s Roundabout Accident Experience and Economic Evaluation (1.3 MB)

This listing of Maryland’s roundabouts not only provides locations for those who wish to go see a roundabout in action, but also provides information on the size and the number of vehicles that use each roundabout. A glance at the chart will show that Maryland has used roundabouts on a wide range of roads from low volume rural intersections (to reduce right-angle accidents) and to settings where the traffic counts exceed those at the infamous Five Points. (202/309/463 intersection in Montgomery County, PA):

Maryland Roundabouts (.15 MB)

These studies and articles by Insurance Institute for Highway Safety (the same folks who have won our trust with their excellent offset car crash testing program) focus on the effectiveness of roundabouts in reducing crash related losses:

Crash Reduction Following the Installation of Roundabouts (.5 MB)

IIHS Roundabout Status Report-1 (.4 MB)

IIHS Roundabout Status Report-2 (.25 MB)

This 6 page guide is an overview to their extremely comprehensive and very technical Roundabouts: An Informational Guide. In this report, the FHWA not only condones but encourages the use of roundabouts in certain situations and provides engineering criteria for their construction. Because of the size of the file, we recommend that you access the full guide via the following link to the FHWA site - http://www.tfhrc.gov/safety/00068.htm . If the link disappears, let us know as we do have the full version saved on our server:

Federal Highway Administration Roundabout Informational Guide (Brief) (.35 MB)

The FHWA also has available a slightly dated overview of roundabouts that focuses primarily on European experience that makes interesting reading for those who are really interested in the subject:

FHWA Overview

Even though Pennsylvania does not have any roundabouts as of yet, and roundabouts have been thoroughly dismissed as an option by District Six (Southeastern PA.), the more intelligent minds that occupy PennDOT’s central administration have recognized the important role that roundabouts can play in Pennsylvania’s future. This guide provides both an overview as well as specific engineering information for their construction:

PennDOT Guide to Roundabouts (2.2 MB)

Although much of the focus in the discussion on roundabouts centers on reduced accident rates for motor vehicles, this 50 page study which was prepared for the Southeastern Transportation Center, looks at roundabouts from the perspective of pedestrian safety:

The Effects of Roundabouts on Pedestrian Safety (1.5 MB)

This is an excellent site that has a wealth of information and photographs of roundabouts. Make sure to click on “Articles” to see how other communities are approaching roundabouts:

Roundabouts USA

Another great roundabout site with history, photos and discussion of roundabout design:

Alaska Roundabouts

Diagrams and information on Clearwater Florida’s large roundabout. This roundabout clear illustrates the need for good design. When originally constructed, it had serious design flaws that caused it to function improperly and accidents went up dramatically. Corrections to the design were made and the accident rate plummeted to near zero:

Clearwater Florida's Roundabout

Roundabout Responses

Oregon has been one of the leaders in the US in the use of roundabouts. Their website provides photographs, videos and information that may be helpful:

Oregon Department of Transportation

The Center for Transportation Research and Training at Kansas State University has created an excellent site that includes photos and videos of various roundabouts:

The Center for Transportation Research and Training

Akcelik & Associates of Australia has provided an excellent site on roundabouts that focuses on both general and professional-only level technical information. Scroll down to the bottom of the opening page and you will find one of the best selections of technical articles available anywhere on the Internet. Many of the photos are from Australia where they drive on the “wrong” side of the road. If this will confuse you then it is best not to visit this site but be aware that you will miss some very interesting material:

Australian Roundabouts