Vertical Curve Length – A Transition Curve

• Passing Sight Distance (S)

  m ft

• Initial Grade (g₁)

  %

• Final Grade (g₂)

  %

•  

• Minimum Curve Length (L_m) in meter

  

• Minimum Curve Length (L_m) in foot

  

Formula:

L_m = [ S² × (g₂ − g₁) ] / 864 ∀ S<L_m

L_m = 2S - [ 864 / (g₂ − g₁) ] ∀ S>L_m

Where,

   

   L_m - Minimum Curve length

   g₁ - Initial grade

   g₂ - Final grade

   S - Passing Sight Distance

Vertical curves are important elements in geometric design of highways, providing transition between two sloped roadways. These are parabolic curves and are assigned stationing based on horizontal axis.