County, State, and National Roundabout Design Guides
Compilation by Joe Mehaffey
This page can be printed from:  http://gpsinformation.info/roundabout/Guides/USA_RoundaboutDesignGuideCompilation.html

Roundabouts are becoming widely used throughout the world at road intersections.  This is because, when they are designed properly, they work well for drivers, provide increased safety,  speed traffic movement, and are a often a lower maintenance cost than traffic lights and other intersection types. 

I am an Engineer and got interested in the design details of roundabout construction as a result of the first one in my own county being put in on a 4-way intersection with 50mph approaches and with the roundabout being designed as a MINI-roundabout size of 74ft diameter but WITH a raised island in the center.  This small "city size" roundaboout  makes it difficult for larger trucks and RVs and  buses to navigate.  During my research, I found the documents in the following list to be useful. 

For some time, I tried to interest our county engineering people in the thought that our roundabout location was NOT an Urban MINI-roundabut location but rather a RURAL highway Roundabout Location.  I suggested that they should put in some fixes to at least make it a bit easier to traverse by cars and smaller trucks.  I was told repeatedly that the roundabout was "all designed OK".  Unfortunately,  there are major conflicts with generally accepted roundabout guidelines as presented in the USDOT Roundabout Guide.  Recently, a wise old road engineer suggested that, in our litigous society,  it would be virtually impossible for a government engineer or company working for a government to readily admit that anything they had a hand in designing could be even slightly mis-designed.  After thinking about that for awhile, that could be the situation in this case.  In case you are curious as to what this roundabout's problems are,  CLICK HERE

So..  While I am giving up on getting any fixes into the present roundabout design,  I will move on to trying to see that FUTURE roundabout designs in our county and state are more carefully considered against the US DOT Roundabout Design Guidelines.  I recommend that everyone reading this consider presenting this thought to your City/County/State governments and elected representatives as well. There is no sense in having EVEN ONE poorly designed roundabout when the USDOT has done such a nice job in providing wide ranging roundabout design guidelines.  Here are some of the more useful documents that I have found.

Many states, counties, and municipalities already have written Roundabout Design Guides offering guidance to engineers and to elected officials on "How to Design Roundabouts".  As I come across such published guidelines, I will link them on this website.  I believe that it is extremely desirable for states,  counties, and municipalities to have a set of agreed upon roundabout guidelines (as opposed to detailed specifications).  By this means,  any significant deviations from the guidelines can be questioned by elected officials BEFORE a problematic roundabout design goes to the construction stage.

The most comprehensive Roundabout Guide that I have found is the US Department of Transportation Roundabout Guide.  This guide has been adopted by the State of New York and others as a guide for roundabout design.  This guide can be found at: http://gpsinformation.info/roundabout/RoundaboutDesign.pdf

Various State and Municipal Roundabout Guides are listed below. 
The listings are not in any particular order of preference and the data variability can be large.

State of Utah - Tooele County-  Compact but detailed Roundaboout Design Guide Based on the US DOT Guide.  Forsyth County Government should use this one.
State of Illinois - Kane County - Compact but detailed Roundabout Design Guide Based on the US DOT Guide
State of Georgia- GDOT -  Very general discussion of roundabouts with few specific design guidelines for designers.
                                              Photos of many Ga. Roundabouts are shown.  ALL appear considerably larger diameter than the North Forsyth Roundabout.
State of Georgia- Forsyth County -  No published guidelines of any kind  are provided on Roundabout Design for Engineers or for Elected Officials. 
North Forsyth Design Critique  No agreed upon design guidelines has resulted in our first roundabout project which does not meet US DOT roundabout size guidelines for its location.
USDOT NCHRP Modern Roundabout Practice in the US- 1998 - Good reading but the USDOT Roundabout Guide has more design detail information
State of Colorado, City of Colorado Springs 2005 - Good document, not as detailed as most,  Good pictures of Rodel Software Design tool.  State of Va must like it.
State of NC Roundabout Guide - Pictures of Roundabouts
State of Maryland Roundabout Guide -  Good guide. Lots of computational guidance on traffic flow vs various parameters.  Roundabout Justification and Engineer oriented.
US MINI-ROUNDABOUT Guide and Application data - This is the size roundabout we have in North Forsyth.. But.. Ours has a non-transversible island in the middle. 
http://gpsinformation.info/roundabout/Guides/nchrp_rpt_572%5B1%5D.pdf - Likely a LOT more about Roundabout Queueing Theory than you ever wanted to know.


If you have a link to a good Federal/State/County/City   Roundaboout Design Guide, please send a link to Joe Mehaffey and I will include it in the listings.  Thanks.