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Geometric Design of Highways

Geometric Design of Highways. Highway Alignment is a three-dimensional problem Design & Construction would be difficult in 3-D so highway alignment is split into two 2-D problems. Components of Highway Design. Plan View. Horizontal Alignment. Vertical Alignment. Profile View.

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Geometric Design of Highways

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  1. Geometric Design of Highways • Highway Alignment is a three-dimensional problem • Design & Construction would be difficult in 3-D so highway alignment is split into two 2-D problems

  2. Components of Highway Design Plan View Horizontal Alignment Vertical Alignment Profile View

  3. Horizontal Alignment Today’s Class: • Components of the horizontal alignment • Properties of a simple circular curve

  4. Horizontal Alignment Tangents Curves

  5. Tangents & Curves Tangent Curve Tangent to Circular Curve Tangent to Spiral Curve to Circular Curve

  6. Layout of a Simple Horizontal Curve R = Radius of Circular Curve BC = Beginning of Curve (or PC = Point of Curvature) EC = End of Curve (or PT = Point of Tangency) PI = Point of Intersection T = Tangent Length (T = PI – BC = EC - PI) L = Length of Curvature (L = EC – BC) M = Middle Ordinate E = External Distance C = Chord Length Δ = Deflection Angle

  7. Circular Curve Components

  8. Properties of Circular Curves Degree of Curvature • Traditionally, the “steepness” of the curvature is defined by either the radius (R) or the degree of curvature (D) • Degree of curvature = angle subtended by an arc of length 100 feet R = 5730 / D (Degree of curvature is not used with metric units because D is defined in terms of feet.)

  9. Properties of Circular Curves Length of Curve • For a given external angle (Δ), the length of curve (L) is directly related to the radius (R) L = (RΔπ) / 180 = RΔ / 57.3 • In other words, the longer the curve, the larger the radius of curvature R = Radius of Circular Curve L = Length of Curvature Δ = Deflection Angle

  10. Properties of Circular Curves Other Formulas… Tangent: T = R tan(Δ/2) Chord: C = 2R sin(Δ/2) Mid Ordinate: M = R – R cos(Δ/2) External Distance: E = R sec(Δ/2) - R

  11. Circular Curve Geometry

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