(TD) for that division. Work trains are not included in computing
train density; however, their presence and the amount of time they
block the main line can reduce the TD of a rail division. Train
density varies on different divisions, depending on the length and
number of tracks of the main line; number and location of passing
tracks; capacity of yards and terminals; signal and communications
systems; method and procedures of train movement; and availability of
traincrews, motive power, and rolling stock.
On a singletrack line, passing tracks should be from 6 to 8
miles apart so that trains can meet and pass; however, a passing
track within 5 miles of another is not expected to affect train
density.
A ruleofthumb method and a formula for determining train
density for a rail division are presented in the following
subparagraphs. When you do not have enough information on a rail
line, you should use the ruleofthumb method; use the formula when
the values that must be substituted in it are known.
a. Rule of thumb. When the planner does not know the number or
location of passing tracks, the length of the line, or the average
speed at which trains can be operated safely over the line, he uses
the following rule of thumb for train density: on singletrack lines
a TD of 10 and on doubletrack lines a TD of 30 is established.
b. Formula for determining singletrack train density. In a
theater of operations, one track of most doubletrack lines is
cannibalized to maintain one good single track. Cannibalize means to
remove serviceable parts from one item of equipment to install them
on another. The discussions in this text are confined to single
track operations. The following formula may be used to determine
fairly accurately the TD for a specific singletrack railway division
if the factors included in it are known.
Where
TD = train density
NT = number of passing tracks
1 = constant (number of trains that could be run if there
were no passing tracks)
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