design of curves

DESIGN OF CURVES

DOLAT RAM (15CRP25)Mehran University of Engineering and Technology, Jamshoro

CURVESCurves are regular bends provided in the lines of communication like roads, railways etc.They are classified into two main types:1. Horizontal curve2. Vertical curve

HORIZONTAL CURVE

A horizontal curve provides a transition between two tangent strips of roadway, allowing a vehicle to negotiate a turn at a gradual rate rather than a sharp cut.The design of the curve is dependent on the intended design speed for the roadway, as well as other factors including drainage and friction.

Classification of Horizontal CurvesHorizontal curves are commonly classified into 4 types:i) Simple Curveii) Compound Curveiii) Reverse or Serpentine Curveiv) Spiral or Deviation Curve

Simple, Compound, Reverse and SpiralSimple Curve - Curve with single constant radius. Compound Curve – Two or more curves in succession, turning in the same direction. Reverse Curve – Two simple curves with equal radii turning in opposite directions with a common tangent. Spiral or Deviation Curve – Also called transition curves; placed between tangents and circular curves or between two adjacent circular curves having substantially different radii.

VERTICAL CURVE

A vertical curve provides a transition between two sloped roadways, allowing a vehicle to negotiate the elevation rate change at a gradual rate rather than a sharp cut.The design of the curve is dependent on the intended design speed for the roadway, as well as other factors including drainage, slope, acceptable rate of change, and friction.

COMPONENTS OF A CURVER RADIUSPC POINT OF CURVATUREPT POINT OF TANGENCYPOC POINT OF CURVEPI POINT OF INTERSECTIONL LENGTH OF CURVET TANGENT DISTANCELC LONG CHORDE EXTERNAL DISTANCEM MIDDLE ORDINATED DEGREE OF CURVEI DEFLECTION ANGLE

FORMULAS FOR SIMPLE CURVE

STOPPING SIGHT DISTANCEStopping Sight distance is one of several types of sight distance used in road design. It is a near worst-case distance a vehicle driver needs to be able to see in order have room to stop before colliding with something in the roadway, such as a pedestrian in a crosswalk, a stopped vehicle. Insufficient sight distance can adversely affect the safety or operations of a roadway or intersection.