# How To Calculate Minimum Non-Passing Sight Distance -Mathematical Example

30th March 2019**Mathematical Example**

Calculate the minimum non-passing or say stopping sight distance on a highway at a descending gradient of 6% with following data: a) Design speed = 80 Km/h, b) Reaction time of driver = 2.5 Sec, c) Coefficient of friction between tire and road surface = 0.4

## Mathematical Solution

Given,

a) Design speed(V) = 80 Km/h

b) Reaction time of driver(t) = 2.5 Sec

c) Coefficient of friction between tire and road surface(f) = 0.4

d) Gradient (n) = 6%

We know, for descending gradient,

**Stopping sight distance/non passing Sight distance **

= 0.278V.t + V**²**/254(f-0.01n)

= 0.278 ⨯ 80 ⨯ 2.5 + 80**²** / 254(0.4 – 0.01⨯6)

= 129.71 m

**Answer:** Non-Passing sight distance or say stopping sight distance should be 129.71 m.

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