Length of Valley Curve Design Method - Civil Engineering

## Length of valley curve

The length of valley curve is designed on the basis of two criteria:
 Length of Valley Curve
i) The allowable rate of change of centrifugal acceleration of 0.06 m/sec .
ii) The head light sight distance .
The higher of the two values is adopted.

### Length of Valley Curve Design Method

i) The length of valley transition curve (Ls) according to the first criteria is given by the following equation:
Ls = [ Nv3 /C]1/2
Where ,N is the deviation angle,v is speed in m/sec and C is the allowable rate of change of centrifugal acceleration.
The length of valley curve (L) is taken to 2Ls .

ii) The length of valley curve (L) according to the second criteria may be determined for two condition
1. When the total length of valley curve (L) is greater the stopping sight distance.
2. When the total length of valley curve (L) is less than the stopping sight distance.

When the total length of valley curve (L) is greater than the stopping sight distance ,the value of L is calculated from the following equation.
L = NS2 /(2h1 + 2StanÎ±)
Where ,h1 is the height of head light , is the angle of inclination of the beam of light ,S is the stopping sight distance and N is the deviation angle.

When the total length of valley curve(L) is less than the stopping sight distance, the value of L is calculated from the following equation:
L = 2S - (2h1 + 2StanÎ± )/N
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