Q2 Z2,(Q2) Z2(Q2) - Institute for Water Resources - U.S. Army

it was not possible to pursue the question of the length of haul
in this study. Implicitly, then, an average trip length has been
assumed. However, the other three effects have been examined. The
towboat production function, for example, employs dummy variables to
determine productivity shifts between sixteen river districts. Dummy
variables arc also used for each month to capture seasonal output
variations. The direct barge cost and single firm cost studies include
a set of variables for the commodity shipped, as well as the seasonal
and river district variables. . .
When taken together, the results are extremely detailed. That is,
it is possible to determine the marginal cost, at any output level, for
shipments of particular commodities, river districts, and season's (16
river districts, times 12 months, times 6 commodity groups, yields 1152
possible cost estimates). In addition, these costs can be adjusted for
the equipment (towboats and barges) used.
It is impossible to summarize all the results here. The individual
results are discussed in each chapter. In general, it was found that
these variables had significant effects on cost. F-tests were performed
on each group of dummy variables to see if they could be excluded from
the individual regressions. The hypothesis of no significant differences
in the residual regression variance was consistently rejected. The
coefficients were found to generally accord with a priori expectations
as to their signs and magnitudes.
If the barge industry was characterized by perfect competition we
would expect the rate structure to reflect these differences in marginal
cost. Barge rates, however, are not always competitive ones. Many
commodities are, of course, regulated by the ICC and various state trans-
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