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The mega elliptical roundabout is a new idea for intersections on rural multilane highways in the form of an elongated ellipse. Basically, there are no procedures or guidelines for designing the mega elliptical roundabout in the Highway Capacity Manual, Federal Highway Administration guides or the American Association of State Highway and Transportation Officials' 'Green Book'. This research therefore presents the best geometric design scenarios of mega elliptical roundabout intersections at various traffic flows for all intersection entrances. The basis for selecting the best scenarios is to achieve minimum delay time, minimum emissions and minimum fuel consumption. This was studied at the intersection of a six-lane divided highway with a four-lane divided highway when the traffic enters from four approaches. Moreover, this research proposes the cases in which the mega elliptical roundabout is better than an interchange (full cloverleaf), and suggests the best time to make a decision to change from a mega elliptical roundabout to an interchange (full cloverleaf). The study was conducted by using Vissim software (version 10.00-02). In total, 1134 scenarios were analysed. [ABSTRACT FROM AUTHOR]