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CHAPTER 11 HORIZONTAL AND VERTICAL CURVES - 14070_237
Figure 11-3.Elements of a horizontal curve. - 14070_239

Engineering Aid 1 - Advanced Structural engineering guide book
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TYPES OF HORIZONTAL CURVES There are four types of horizontal curves. They are described as follows: 1. SIMPLE. The simple curve is an arc of a circle (view A, fig. 11-2). The radius of the circle determines the sharpness or flatness of the curve. 2.  COMPOUND.  Frequently,  the  terrain  will require  the  use  of  the  compound  curve.  This  curve normally consists of two simple curves joined together and curving in the same direction (view B, fig. 11-2). 3.  REVERSE.  A  reverse  curve  consists  of  two simple  curves  joined  together,  but  curving  in  opposite direction.  For  safety  reasons,  the  use  of  this  curve should  be  avoided  when  possible  (view  C,  fig.  11-2). 4. SPIRAL. The spiral is a curve that has a varying radius.  It  is  used  on  railroads  and  most  modem highways. Its purpose is to provide a transition from the tangent to a simple curve or between simple curves in a  compound  curve  (view  D,  fig.  11-2). ELEMENTS OF A HORIZONTAL CURVE The  elements  of  a  circular  curve  are  shown  in figure 11-3. Each element is designated and explained as follows: PI POINT   OF   INTERSECTION.   The   point   of intersection is the point where the back and for- ward  tangents  intersect.  Sometimes,  the  point of intersection is designated as  V (vertex). I INTERSECTING   ANGLE.   The   intersecting angle is the deflection angle at the PI. Its value is  either  computed  from  the  preliminary traverse angles or measured in the field. A CENTRAL ANGLE. The central angle is the angle  formed  by  two  radii  drawn  from  the Figure 11-2.—Horizontal curves. 11-2







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