Design of median ends at at-grade intersection layout plans

Abstract

Median represents a portion of an urban road separating opposing directions of the traveled way. Due to their function to provide enough space for separate traffic lane and storage of left-turning vehicles, the medians are highly desirable on city arteries carrying two or more lanes per travel direction. Type and dimensions of turning vehicles significantly affect the design of a median openings and median ends. The design solution and the geometry of median ends should be based on the composition of all left-turning movements occurring simultaneously at at-grade intersection. After selection of design vehicles for swept path analysis of the characteristic turning maneuvers in intersection, larger vehicles should be further checked for their ability to turn without undue encroachment on adjacent traffic lanes. The critical design parameter is the median width, especially at the ends of the median openings. Dragging paths of left-turning vehicles shape the median ends geometry. In traditional design practice established in Europe, three-centered compound curves with radii rations R1 : R2 : R3 = 2 : 1 : 3 and R1 : R2 : R3 = 2.5 : 1 : 5.5 are used to approximate dragging pahs of turning vehicles. In this paper, considering the median width, the deficiencies of the traditional design approach are revealed and new findings regarding the design of the median ends at at-grade intersections are presented.