20
2 = constant to convert to one direction
24 = constant (number of hours per day)
S = average speed
LD = length of division
An example of how to use the formula to determine train
density is presented in the next paragraph. It is based upon
pertinent information on a hypothetical railway division.
2.14. EXAMPLE OF TRAIN DENSITY DETERMINATION
You are going to operate a singletrack rail division of 110
miles with a ruling grade of 1.3 percent and track rated good to
fair. Passing tracks are located at the following distances in miles
from the beginning of the division: 7, 15, 21, 27, 31, 37, 45, 53,
60, 66, 74, 81, 85, 91, 97, and 103. With this information and the
formula you can find values for each of the unknowns and determine
the train density. The following subparagraphs discuss each unknown
and illustrate how it is used.
a. Number of passing tracks (NT). As stated earlier, passing
tracks should be at intervals of 6 to 8 miles along the main line. A
passing track within 5 miles of another one should not be counted
when determining TD because two passing tracks that close together do
not increase TD. In the formula, the value you should substitute for
NT for this hypothetical division is 14. Notice that this value is
two less than the number of passing tracks given; but, two of them,
those at mileposts 31 and 85, are within 5 miles of the tracks
immediately preceding them and should not be counted.
b. Average speed (S). Table IV presents average speed values for
different conditions of track and percentages of ruling grade.
Experience with previous military railway operations has proved these
factors to be accurate enough for determining TD. You know that your
division is rated good to fair and that the ruling grade is 1.3
percent. From the table you determine that the average speed of
trains for a singletrack rail line rated good to fair with a ruling
grade of 1.5 percent or less is 10 mph. Remember that the most
restrictive factor is used to govern the selection of the average
speed. For example, if the track was rated good to fair but the
ruling grade was 2.0 percent, the grade factor would be the most
restrictive and the average speed would be 8 mph.
Previous Page
