the forward-movement time of the four trains is 24 hours--l0 hours
running time, 10 hours unloading time, 1 hour between trains, and 1
extra hour for any unexpected delay. The rear-movement time is also
24 hours, assuming that loading time at the port terminal is 10
hours; again, 1 extra hour is allowed for unforeseen delays.
This is how the schedule might work out.
Train No. 1 would
leave the port terminal at midnight and arrive at railhead A at 1000
hours; train No. 2 would leave at 0100 hours and arrive at 1100
hours; train No. 3 would leave at 0200 hours and arrive at 1200
hours; and train No. 4 would leave at 0300 hours and arrive at 1300
hours.
Since unloading would begin on each train as it arrived at
the railhead, all four trains would be unloaded by 2300 hours.
Leaving 1 hour for unforeseen delays, train No. 4 would be the first
to leave the railhead at midnight and begin the empty run back to the
port terminal. It would be followed at 1-hour intervals by the other
three trains in reverse order from their forward movement. When they
arrive at the port terminal, they would be loaded and ready to begin
a return trip at midnight on the following day.
This completes the
first cycle of fleet operation; it is tabulated below.
Fleet Operation from Port Terminal to Railhead A
With extra locomotives and rail cars at the port terminal, four
other trains could already have been made up and be ready to depart
when the last empty train arrived.
Thus, a new cycle could be
started immediately after the last empty train arrived at the port
terminal, eliminating the delay of 11 hours.
The fleet method is limited by the capacity of forward terminals
or railheads to receive and unload cars; this lowers the number
of locomotives and cars that can be used.
For instance, since
railhead A can accommodate only four trains at one time, many
locomotives and cars may be standing idle that might otherwise
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