Roundabouts have caught the imagination of the public. They are perceived to be less obtrusive and more efficient than conventional un-signalized or signalized intersections. Transportation planners recognize that roundabouts have distinct advantages under many circumstances, but they are reluctant to commit to this still uncommon type of control. The purpose of our research was to provide additional circumstances and "rules of thumb" where roundabouts are superior to conventional intersections. For example it has been well documented that in undersaturated conditions roundabouts result is less delay than conventional intersections. But where is the line for undersaturated conditions under varying circumstances? Also, how is this conclusion affected by unfamiliar drivers or platoon arrivals? To answer these questions the author summarized several guidelines and conducted simulations of roundabouts using the AIMSUN NG microsimulation. The simulations generally focused on observing performance at or near saturated conditions. Field observations of these conditions are difficult, both because they are not common and because of the unstable nature of traffic near capacity. In the controlled "field" environment of a microsimulation the author did not have these difficulties. He was able to observe roundabouts side-by-side with a similar intersection under varying mixes of traffic, driver behavior, arrival type and roundabout geometry. Using these results the author presents general rules of thumb to aid planners in their interactions with the public, engineers and elected officials.
Abstract