Table II. Average Values of Rolling Resistance (RR)

As shown in table II, the poorer the track the higher the

resistance factor that must be used in determining how much weight

you can attach behind a locomotive and expect it to pull. For

example, the value of RR is 7 pounds per ton of train for fair to

poor track. This means that for each ton of a train, 7 pounds of

force must be used to overcome rolling resistance.

2.7. GRADE RESISTANCE

The resistance to the progress of a train offered by a grade is

called grade resistance (GR); caused by gravity, it tends to pull the

train downhill. In the formula that follows, grade resistance is

shown as being equal to 20 pounds per ton of train for each percent

of grade. This means that 20 pounds of force must be exerted to move

1 short ton of train up each 1 percent of grade. In railroading, the

percent of grade is an expression of the number of feet of vertical

rise per 100 feet of horizontal distance. For example, if a 100foot

section of track rises 2 feet, the percent of grade for that section

is 2. In planning for the operation of trains, the military planner

is primarily interested in the maximum or ruling gradethe grade

that limits the tonnage a locomotive can pull. Therefore, the

percent of grade given in the formula is an expression of the amount

of rise per 100 feet of the ruling grade for a given rail line.

Grade resistance, then, is found by multiplying 20 pounds per ton of

train by the percent of the ruling grade.