The Transportation Research Board’s (TRB) National Cooperative Highway Research Program (NCHRP) Report 672: Roundabouts: An Informational Guide – Second Edition is an update from the original roundabout informational guide released in 2000 by the U.S. Federal Highway Administration. The report assists transportation professionals in explaining trade-offs associated with roundabouts and reviews the planning, design, construction, maintenance, and operation of roundabouts.