Set Back Distance & Curve Resistance

Curve Resistance: The loss of tractive force due to turning of a vehicle on a horizontal curve.

  =T ( 1- Cosθ)

Where θ = Turning angel,

T = actual tractive force.

>> Curve resistance develops only in vehicles having Rear driving wheels.

>> Curve resistance is acute in hill roads.

Set Back Distance (M): “Setback” or the “clearance” is the distance required from the center line of horizontal curve to an obstruction on the inner side of the curve to provide adequate sight distance at a horizontal curve.

Factors Affecting:

>> Sight distance desired (OSD, lSD and OSD),

>> Length of curve

>> Radius of horizontal curve.

Approximate Formulae:

Case 1: When length of curve is more than the sight distance

m = s²/8R

Case 2: When length of curve s less than sight distance

m = L (2S-L)/8R