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For a portion of national highway where a descending gradient of 1 in 25 meets with an ascending gradient of 1 in 20, a valley curve needs to be designed for a vehicle travelling at 90 kmph based on the following conditions.

(i) headlight sight distance equal to the stopping sight distance (SSD) of a level terrain considering length of valley curve> SSD.

(ii) comfort condition with allowable rate of change of centrifugal acceleration = 0.5 m/sec³.

Assume total reaction time = 2.5 seconds; coefficient of longitudinal friction of the pavement= 0.35; height of head light of the vehicle =0.75 m; and beam angle = 1°.

What is the length of valley curve (in m) based on the head light sight distance condition? __________

308 to 311

213 to 216

578 to 581

435 to 438

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