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Transportation Engineering 2010 Fall Semester

Geometric Design of Highways

• Horizontal Curve • Vertical Curve

Horizontal Curve • Horizontal Alignment

– Straight sections (tangent) – Curves

• Horizontal Curve – Directional transition of the roadway in a horizontal

plane. – Transition between two straight (or tangent) sections of

roadway. • Four types of horizontal curves:

– simple – compound – reversed – spiral

Simple Horizontal Curve

Garber and Hoel, Traffic and Highway Engineering, Cengage Learning, Forth Edition, 2009

Compound Curve

Garber and Hoel, Traffic and Highway Engineering, Cengage Learning, Forth Edition, 2009

Reverse Curve

Garber and Hoel, Traffic and Highway Engineering, Cengage Learning, Forth Edition, 2009

Horizontal Curve Fundamentals

• R: Radius • PC: Point of Curve • PT: Point of Tangent • PI : Point of

Intersection

Horizontal Curve Fundamentals

• Tangent Length – T=R tan Δ/2

• Long Chord Length – C=2R sin Δ/2

• Curve Length – L=RΔπ/180

Horizontal Curve Fundamentals

• Sharp or Smooth? – By Radius – By Degree of Curve

• Degree of Curve – Arc Definition – Chord Definition

Min. Radius of Circular Curve

• Centrifugal Force (원심력) • Centripetal Force (구심력) • Superelevation

Min. Radius of Circular Curve

Garber and Hoel, Traffic and Highway Engineering, Cengage Learning, Forth Edition, 2009

Min. Radius of Circular Curve

127
*R:m, u:km/h, g=9.8m/s2
*

*R:ft, u:mi/h, g=32.2ft/s2
*15

tan

cos cos

= acceleration for curvilinear motion = /R (R=radius of the curve) W = weight of the vehicle g = acceleration of gravity

Horizontal Sight Distance

Example S=180m, R=800m M=?

Line of Sight

Sight Distance

M

R