The main focus of this dissertation is the development of solution procedures
for these optimization models. Their computational complexity makes the use of
heuristics solution procedures advisable. One of the heuristics we propose is a Multi-
Commodity Dynamic Slope Scaling Procedure (MCDSSP). This heuristic makes use
of the fact that when minimizing a concave function over a convex set, an extreme
point optimal solution exists. The same holds true for linear programs. Therefore,
the concave cost function is approximated by a linear function and the corresponding
linear program is solved.