Mega elliptical roundabouts versus grade-separation interchange

Abstract

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.

A Novel Methodology for Estimating the Capacity and Level of Service for the New Mega Elliptical Roundabout Intersection

“…Mega elliptical roundabout is a new intersection. Its form is an elongated ellipse combining the best functions of the roundabout and the unconventional median U-turn (UMUT) intersection [5].…”

“…Moreover, the form of this island is an ellipse that has an ellipse element (b) for providing a suitable basic ellipse roadway radius in order to be appropriate for heavy vehicles that make a U-turn on basic ellipse roadway. e second feature is the ellipse roadway, which has three parts: the basic ellipse roadway, weaving sections, and nonweaving sections [5].…”

“…(1) As described in Section 2, most researchers estimated roundabout capacity in terms of entry capacity. However, the mega elliptical roundabout differs from a roundabout in traffic operations [5]. (2) Researchers who analyzed the roundabout from the viewpoint of the weaving section did not calibrate their method.…”

“…us, there is a great need for alternative intersections offering the potential to reduce delay, improve safety, and reduce the influence on the environment with fewer effects and a lower cost than traditional solutions [1][2][3][4]. erefore, the authors proposed a new type of intersections which is called "mega elliptical roundabout" in a previous paper [5]. Totally, they analyzed 1134 scenarios by VISSIM software to analyze the initial feasibility and determine the best scenarios of geometric design for mega elliptical roundabout intersections.…”

“…e empirical models are generally better but cannot be used to analyze mega elliptical roundabout at present because mega elliptical roundabout is a new type of intersections, so no field data are available, while the initial feasibility analysis of mega elliptical roundabout has been introduced in another work by simulation models [5].…”