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.