From Engineering Policy Guide
A roundabout is a circular traffic intersection featuring yield control on all entering roadway legs, one-way continuous flow within the circulatory roadway, channelization of the approaching roadways, and appropriate geometric curvature to keep circulating speeds low. Roundabouts may contain as few as three legs; however, roundabouts with more than four legs are not uncommon. Typical roundabout terminology with key geometric elements is available.
This article is currently under comprehensive revision to more accurately reflect the contents of TRB’s NCHRP Report 672, Roundabouts: An Informational Guide, Second Edition. In the interim, that guide is considered the location selection, design and layout guidance for MoDOT roundabouts.
In order to ensure Missouri’s roundabouts are designed according to the current practice and provide for a functional and operational analysis, all preliminary roundabout layouts shall be submitted to both Traffic Division and Design Division for review prior to detailed design.