Question

A major road with a design speed of 90km/h intersects a minor road whose design speed is 50km/h. If the right of way of the main road is 20m while that of the minor road is 10m and that the two roads are perpendicular to each other, calculate the size of the sight triangle.

NOTE: The right of way is measured from the centre of the road. (According to TRH170

Answer 1

If we want to pictorially represent the above problem we can do so as follows

So we need to calculate the lengths of ab bd and ac.

We know that stopping sight distance can be calculated as

Minimum SSD will happen when the reaction time is zero. So assume reaction time is zero since the problem anyways doesnt mention it. Also friction coefficient is zero, since we are not given any information about it. Assume grade is also zero

so SSD = v²/2g

For major road , v = 90kmph = 25 mps, for minor road v = 50kmph = 13.89 mps

so SSD_major = 25²/2*9.8 = 31.89m

SSD_minor = 13.89²/19.6 = 9.843m

Therefore ab = 31.89m, bc = 9.843m, and we can calculate ac by pythogras theorem as sqrt(31.89 + 9.843² ) = 33.375m

So our sight triangle is as follows

So on the major road the car should be atleast 26.89m from the stop line

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