Figure 3-1. Combining Curves

d. Curve Resistance. Curvature adds to propulsion resistance at an average rate of 0.8 lb for each ton

of train weight for each degree of curve. As a 1-percent grade adds resistance of 20 lb per ton, a one-

degree curve is then equivalent (in resistance) to 0.04-percent grade.

e. Curve Compensation.

(1) When laying out a route, the additional resistance due to curvature must be accounted for in the

design. This procedure is known as curve compensation. Compensating a grade for curvature is almost

always required for ruling grades, and is recommended for grades in moderate and higher categories.

(Curve compensation is sometimes omitted where curves are very short or of gradual degree).

(2) Where curve compensation is needed, grades on curved track will be reduced by the following:

Eq. 3-1

Gr = Amount of grade reduction (percent).

D = Degree of curvature (decimal degrees).

(a) Actual and Effective Grade. Table 3-4 illustrates curve compensation for a 1-percent grade. As

shown, if a train travels around a long curve of 4 degrees on a 1-percent grade (uncompensated), the

combined resistance is equal to a 1.16-percent grade. To maintain an effective grade (as experienced by

the train) of 1-percent, the actual grade constructed through the 4-degree curve must be limited to 0.84-

percent. Since the actual grade is reduced, compensating for curvature requires a longer track length to

reach a given elevation.

3-3