A database that includes over 5000 modern roundabouts in America.
http://www.mediafire.com/download/e9ch50iu2afkh4x/Modern+Roundabouts+%28May-2015%29.kmz
The modern roundabouts are categorized into two major classes. To be categorized as an "A" class roundabouts, the following characteristics need to be met:
*Traffic yields at entry.
*Raised splitter islands included at all legs of the roundabout.
*Splitter islands deflect vehicles sufficiently to slow entering traffic.
*Truck apron present to allow more room for large vehicles to navigate the roundabout.
*Proper pavement striping and signage to direct vehicles through the roundabout.
*Central island of roughly 50-200 feet in diameter.
*Pedestrian crossings include a refuge area within the splitter island.
If one or more of these characteristics are not met, it is classified as a "B" class roundabout. While somewhat subjective, classifying attempts to highlight the well designed modern roundabouts in America.
You missed one here (http://goo.gl/maps/bGuwv) in Huntsville, AL.
And there may be a 5,004th roundabout if GDOT have their way. That would be near rural Hephzibah, Ga. along GA 88. www.wjbf.com/story/26500564/-dangerous-south-augusta-intersection-could-be-considered-for-roundabout
Updated the roundabout database for May 2015. Current number stands at 5,125.