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Sight Distance Questions and Answers

1.

The stopping sight distance on a level highway road is 61.4 m, done for two-way traffic with two lanes. What is the stopping sight distance for the highway if two-way traffic with a single lane is considered?

Exam Year(s)

DSSSB JE - 2023,

Answer: C

The stopping sight distance is 61.4 m for a two-way road with two lanes. On a single-lane road with two-way traffic two vehicles approaching each other on the same lane must each be able to stop before they meet, so the sight distance required is double that for a single vehicle:

\[ 2 \times 61.4 = 122.8\ \text{m} \]

The value of 61.4 m is the case already given for two lanes, and 30.7 m is half of it, which is the wrong way round. The value 150.8 m does not follow from the data.

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2.

As per IRC66 : 1976, the intermediate sight distance should be:-

Exam Year(s)

RSMSSB JE - 2025, RSMSSB JE Agriculture - 2025, RSMSSB - 2025,

Answer: D

As per IRC 66, intermediate sight distance is 2 SSD.

Intermediate sight distance is twice the safe stopping sight distance. It is provided on two-lane roads where full overtaking sight distance cannot be given, so that drivers have a reasonable chance to overtake with caution.

(SSD + OSD)/2 and (OSD - SSD)/2 are not defined sight distances, and 2 OSD would be longer than the overtaking distance itself, which defeats the purpose of an intermediate value.

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3.

The safe stopping sight distance for a given road is 120m and passing distance is 250m. The intermediate sight distance is:-

Exam Year(s)

RSMSSB JE - 2025, RSMSSB JE Agriculture - 2025, RSMSSB - 2025,

Answer: A

The intermediate sight distance is 240 m.

By IRC practice, intermediate sight distance is twice the safe stopping sight distance.

\[ \begin{aligned} \text{ISD} &= 2 \times \text{SSD} \\ &= 2 \times 120 = 240\ \text{m} \end{aligned} \]

The passing (overtaking) distance of 250 m is not used. 500 m is twice the passing distance, 250 m is the passing distance itself, and 120 m is the stopping distance.

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4.

As speed increases, longitudinal friction coefficient:

Exam Year(s)

RSMSSB JE - 2025, RSMSSB - 2025,

Answer: A

As speed increases, the longitudinal friction coefficient Decreases.

At higher speeds the tyre has less time to grip the micro-texture of the pavement and, on wet roads, a film of water builds up under the tyre, so the available friction falls. IRC therefore uses longitudinal friction coefficients of about 0.35 to 0.40 for stopping sight distance, the lower values for higher design speeds.

Friction does not stay constant or rise with speed; that is why stopping distances increase faster than speed itself.

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