Question

The existing posted speed limit on a section of highway is 88 km/h and studies have shown that the current 85th percentile speed is 104 km/h. If the posted speed limit is to be increased to the current 85th percentile speed, what should be the increase in the radius of a curve that is just adequate for the existing posted speed limit? Assume a superelevation rate of 0.08 for the existing curve and for the redesigned curve.

Answer 1

Solution:-

Given

Initial speed = 88 km/h

New speed = 104 km/h

super elevation = 0.08

Formula used

R = Radius of curve

e = super elevation

= coefficient of side friction

From the standard value at 85 km/h

side friction = 0.13

and at 104 km/h ,   = 0.1

For

Increase in radius = (290 - 473.14) km

= 183.1 km