divisions of railroad between the port and the railhead. Also, all
divisions are assumed to have the same train density and the same
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number of cars per train, because the bulk of all cargo moved in a
theater is through freightfrom port to railhead.
To find the number of cars, by type, required for 1 day's
dispatch, divide the number of short tons to be transported in each
type of car by the average payload of these cars. An example of how
to determine 1 day's dispatch is given in paragraph 3.5.
When you know the number of cars in 1 day's dispatch, you can
determine the total number of cars required for the entire operation.
To do this, you must first know the turnaround time, the total
estimated number of days required from the time a car is placed for
loading at its origin, moved to its destination, unloaded, and
returned to its origin. Such time is computed as follows: allow 2
days at origin, 2 days' transit time for each division (1 for forward
and 1 for return traffic), and 1 day at destination. This method,
rather than an actual hourly basis, is used to allow for delays due
to switching at terminals and way stations and rehandling of trains
in transit. The total number of cars required for the operation is
determined by multiplying 1 day's dispatch of each type of car by the
turnaround time. Then, to the total number required, add 10 percent
to each type of car as a reserve to allow for contingencies such as
routine maintenance, bad order cars, operational peaks, and delays.
3.5. EXAMPLE OF DETERMINING ROLLING STOCK REQUIREMENTS
Assume that you are planning a rail operation in a theater of
operations. The railroad is the same hypothetical threedivision,
singletrack, standardgage rail line discussed in paragraph 2.17 of
chapter 2. You are not doubleheading or adding more sidings. The
line reaches from a port to a railhead in the forward area of the
theater. You have already determined that the end delivery tonnage
for the railroad is 2,177 short tons. From your intelligence data
you find that the tonnage is to be moved on the following basis: 50
percent of the EDT will be shipped in boxcars, 40 percent in
gondolas, and 10 percent in flatcars. The three types of cars are
all U. S. Army rolling stock with rated capacities of 40 short tons,
or carrying capacities (payload) of 20 STON each. Your problem is to
find how many cars, by type, are required to operate the railroad.
First, you must find a value for 1 day's dispatch (DD). This
computation is important, because subsequent switch engine
requirements are based on 1 day's dispatch. Remember that in broad
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