Just found this presentation that a MnDOT engineer gave to the Minneapolis Pedestrian Advisory Committee:
http://www.ci.minneapolis.mn.us/pedestrian/PAC_Roundabout_Presentation_2009_08_05.pdf
It includes a slide showing that Urban Compact Roundabouts can be 80′-100′ and have an average capacity of 15,000 vehicles per day… perfect for Nicollet Ave.
