Vertical Cerves(Crest)

O K value

• What is a K value?
  • It's a number that describes the size of a vertical curve on a road.
  • It tells how many meters of curve are needed for every 1% change in slope.
• Why use K values?
  • They make it easy to calculate the curve's radius at the top: R=100K.
  • The radius and K value give almost the same result for normal road slopes.
• How are K values used?
  • Road authorities might give you the K value to use.
  • If not, you calculate it based on the road’s shape and stopping sight distance.

O Minimum Length of Vertical Curves

 

• When Grade Changes Are Less Than 1%:
  • The calculated curve lengths may be impractically short for construction.
  • In such cases, choose one of the following options:
    1. Design without a vertical curve: If the grade change falls within the range specified in Table 8.12, a vertical curve may be omitted.
    2. Use minimum vertical curve lengths: Refer to the values defined in Table 8.10.
  • Note: Some road agencies mandate vertical curves for all grade changes on major road alignments.
• Curve Length Calculation:
  • The values in Table 8.10 should not be used if the formula L=KA results in longer curves.
  • These minimum values should only apply when they exceed the distance derived from the formula.

 

O  Maximum Grade Change without a Vertical Curve

• Permissible Grade Change:
  • Grade changes equal to or below the limits listed in Table 8.12 do not require a vertical curve.
  • Standard construction techniques ensure sufficient rounding for appearance and ride comfort.
  • However, deliberately using a series of small grade changes to avoid a vertical curve is not an acceptable design approach.