Horizontal alignment curve The horizontal alignment consists of

Horizontal alignment (curve) The horizontal alignment consists of straight sections of the road (known as tangents) connected by curves. The curves are usually segments of circles, which have radii that will provide for a smooth flow of traffic. 1

Horizontal Curve Fundamentals PI T Δ E M PC L Δ/2 R PT R Δ/2

Horizontal Curve Fundamentals PI T Δ E M PC L Δ/2 R PT R Δ/2

Horizontal alignment (curve) D is the “degree of curvature” which is the horizontal angle opposite to (a) radius curve of 100 m or 100 ft long (arc definition), or (b) chord of 100 m or 100 ft long (chord definition). 4

Horizontal alignment (curve) 5

Field Location of a Simple Horizontal Curve Simple horizontal curves are usually located in the field by staking out points on the curve using angles “deflection angles” measured from the tangent at the point of curve (PC) and the lengths of the chords joining consecutive whole stations. 6

Field Location of a Simple Horizontal Curve 7

Field Location of a Simple Horizontal Curve 8

Example: A horizontal curve with degree of curvature of 4 o and intersection angle of 55° 25’, the PC is located at station 238 +44. 75. Determine the length of the curve, the station of the PT, station of PI, the chord length, tangent length, the external and internal ordinates. Answer: 9

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Example: A horizontal curve with degree of curvature of 4 o and intersection angle of 55° 25’, the PC is located at station 238 +44. 75. Determine the deflection angles and the chord lengths for setting out the curve at whole stations from the PC. 12

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