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The next step is to determine the net trainloadthe weight of
the payload or freight carried by a train. Military planners use a
value of 50 percent of the gross trailing load to determine NTL.
Train density, the number of trains that can be safely operated
over a rail division in each direction during a 24hour period, may
vary with each division of rail line, depending on the
characteristics of each. If enough intelligence data on the rail
line are available, the planner uses a formula that takes into
account the number of passing tracks, average speed, and length of
division in determining train density. However, in the absence of
sufficient information, military planners use the rule of thumb which
allows a TD of 10 for singletrack and 30 for doubletrack lines.
The next thing a planner figures is net division tonnagethe
tonnage or payload in short tons that can be moved over a rail
division each day. Computed separately for each division of rail
line, NDT is found by multiplying the net trainload by the train
density for each division.
The final step in determining rail line capacity is the end
delivery tonnage, or the through tonnage of payload that can be
delivered at the railhead each day. In an allrail movement, the end
delivery tonnage is the same as the NDT of the most restrictive
division of the railroad.
Once the tonnage capacity of a rail line has been determined,
the next thing a planner needs to know is how to determine the amount
and types of equipment required to operate the railroad at maximum
capacity.
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