# Length of Summit Curve Design Method

## Length of Summit Curve

The length of the summit curve is designed based on the two criteria:

i) Considering the stopping sight distance.
ii) Considering the safe overtaking sight distance or intermediate sight distance.

### i) Considering the Stopping Sight Distance

The length of summit curve(L) according to this criteria may be determined for the two conditions:

a) When the total length of the summit curve (L) is greater than the stopping sight distance(S).

b) When the total length of the summit curve (L) is less than the stopping sight distance.

When the total length of the summit curve (L) is greater than the stopping sight distance, the value of L(length of summit curve) is calculated from the following equation:

L = NS/(√2H + √2h)2

Where,
H = is the height of eye level of the driver above the roadway surface in m.
h = is the height of the object above the pavement surface in m and N is the deviation angle.

When the total length of the summit curve (L) is less than the stopping sight distance, the value of L(length of summit curve) is calculated from the following equation:

L = 2S – (√2H + √2h)/N

### ii) Considering the safe overtaking sight distance or intermediate sight distance

The length of summit curve(L) according to this criteria may be determined for the two conditions:

a) When the total length of the summit curve (L) is greater than the overtaking or intermediate sight distance (S).

b) When the total length of the summit curve (L) is less than the overtaking or intermediate sight distance (S).

When the total length of the summit curve (L) is greater than the overtaking or intermediate sight distance (S), the value of L is calculated from the following equation:

L = NS2/8H

When the total length of the summit curve (L) is less than the overtaking or intermediate sight distance (S), the value of L is calculated from the following equation:

L = 2S – 8H/N

Length of Valley Curve

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