For smaller radius curves smaller than 200m or greater curvatures andor

# For smaller radius curves smaller than 200m or

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For smaller radius curves (smaller than 200m) or greater curvatures and/or narrower pavements, widening is normally from 0.6 to 1.2m, depending on design speed and pavement width. Pavement widening less than 0.6m is not recommended.
Lecture 5 13/04/14 6 Design of Horizontal Alignment Compound Curves Compound curves consist of two or more curves in succession, turning in the same direction, with any two successive curves having a common tangent point. Compound curves are used mainly in obtaining desirable shapes of horizontal alignment, particularly at at-grade intersections, ramps of interchanges, and highway sections in difficult topographic conditions. To avoid abrupt changes in alignment, the radii of any two consecutive simple curves that form a compound curve should not be widely different. AASHTO recommends that the ratio of the flatter radius to the sharper radius in open highways should not be greater than 1.5:1. The maximum desirable is 1.75:1. In cases where ratios higher than 2:1 are to be used, a spiral curve should be placed between the simple curves.
Lecture 5 13/04/14 7 Design of Horizontal Alignment Reverse Curves Reverse curves may also be designed under constraints in difficult topography. They usually consist of two simple curves with equal radii turning in opposite directions with a common tangent. Reverse curves are usually not recommended because sudden changes to the alignment may result in drivers finding it difficult to keep to their lanes. When it is necessary to reverse the alignment (I.e. if reverse curves must be used) it is recommended that the two simple horizontal curves are separated by a sufficient length of tangent to achieve full superelevation. Alternatively, the simple curves may be separated by an equivalent length of spiral or transition curve
Lecture 5 13/04/14 8 Design of Horizontal Alignment

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