Highways Design: Grade compensation

Grade compensation

While a vehicle is negotiating a horizontal curve, if there is a gradient also, then there will be increased resistance to traction due to both curve and the gradient. In such cases, the total resistance should not exceed the resistance due to gradient specified. For the design, in some cases this maximum value is limited to the ruling gradient and in some cases as limiting gradient. So if a curve need to be introduced in a portion which has got the maximum permissible gradient, then some compensation should be provided so as to decrease the gradient for overcoming the tractive loss due to curve. Thus grade compensation can be defined as the reduction in gradient at the horizontal curve because of the additional tractive force required due to curve resistance (T cos? ), which is intended to o set the extra tractive force involved at the curve. IRC gave the following specification for the grade compensation.

1.       Grade compensation is not required for grades    flatter  than 4%    because the  loss of  tractive force is negligible.

2.       Grade compensation is  30+R %,  where R  is  the radius of the      horizontal   curve in meters.

3.       The maximum grade compensation is  limited to  75R %.