VIAL—GRADE    REDUCTION.                                    67

A PECULIAR INSTANCE OF GRADE REDUCTION.
 

By F. K. Vial, '85, Asst. Civil Engineer Belt Railway, Chicago.
 

My attention was recently called to what at first appeared to be,
if true, a peculiar instance of grade reduction. It occurred on the
Belt Railway of Chicago.

The road was built to furnish a simple and rapid means of trans¬
ferring freight cars from one road to another. The general surface
of the ground upon which the road-bed rests is practically level, but
it was necessary to carry the grade over the important railroads, and
as is usually the case with new roads, the grades were rather heavy.
The traffic has become heavy and trains of great length are hauled.
The ruling grades are of course the approaches to the viaducts,
one of which is over the C. B. & Q. R. R., at Hawthorne. The south
approach to this viaduct was originally a 1% grade, but was recently
changed to a 0.54% grade, when it was found that there was no ap¬
parent benefit to operation, but rather a detriment, inasmuch as the
change necessitated a reduction in the length of train previously
handled.

It is my purpose to analyze the problem in a general way and to
show that the original grade line was an easier operating grade, for
long trains, than the new grade. It is not my intention to arrive at
exact results, but only to show the reason why the new grade does
not benefit operation in proportion to the change. For convenience
of calculation I will use only round numbers and will not adhere to
the exact profile.

It will answer our purpose to suppose a grade, B C, Fig. 1,
page 30, 2 400 feet long rising 24 feet above the horizontal, with
100 feet level at the summit, CD, and then a descent by a 1% grade
to the original level.

The grade on the south side was changed to about 0.5%,
so we will call the new grade 4 800 feet long, at the foot of which
the Chicago, Madison and Northern Railway crosses at grade, as
shown in the diagram.

Suppose a train of 100 empties, weighing 18 tons per car, has come
to a stop for this crossing. Let us find how much power would be re¬
quired to carry it over the old grade. ^ It has been shown by experi¬
ment that freight trains require about 6 pounds tractive
force per ton to overcome the resistance of friction on a level track,
and as the train begins to ascend a grade the resistance increases ac¬
cording to the well known laws of the inclined plane.    Thus, the in-