## 6 Conclusions  
The results illustrate many interesting things: First and most noteworthy is that the hub strategy can be a profitable activity if the hubs are put into operation. In the experiments, we varied everything that could reasonably be changed, and even in scenarios with low attractiveness (low quantities handled by the hubs) and low margins, the business was still profitable. For example, in the baseline, the estimate weekly net profit is USD 951,000 which corresponds to an average weekly net profit of around USD 40,000 per hub. The total costs in this baseline scenario, calculated from Figure 5, are USD 360,000. In this case, the weekly net profits are almost three times the total costs. In the extreme case of the lowest value of sensitivity to distance (\(\gamma\)) and the highest fixed costs, the weekly net profit is USD 372,000 and an average weekly net profit of around USD 31,000 per hub. In terms of factors that affect the profitability, the sensitivity exponent appears to be the most important as illustrated in Figure 8. For instance, keeping the fixed costs variation constant at 0%, we can observe that the weekly net profits ranged from USD 413,000 to USD 1,201,000 (almost three times). It can also be noticed, in the same figure, that varying the fixed costs produced nearly no variations in the gross profits. Second, as said above, there were scenarios in which the optimal solution resulted in zero (0) open hubs. These were scenarios in which hubs failed to attract farmers (low values of \(\gamma\) and \(\delta\)). This implies that the private (hub concessionaires) and the public institutions (e.g., RAP-E-) have the challenging task of promoting the usage of the hubs (i.e., increase the values of \(\gamma\)). This can be done through education and better trading conditions for farmers. This is not easy for people who have been isolated for years and are reluctant to change their culture and traditions. In our point of view, major attractors would be offering \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Variation in Margin** & **Gross** & **Transport** & **Emission** & **Fixed Operation** & **Net Profit** & **No Hubs** & **Total Handled** \\
**of Gross Profit** & **Profit** & **Costs** & **Costs** & **Costs** & **Quantities (Tons)** & **Quantities (Tons)** \\ \hline Baseline 1\(\times\) & 1310 & 198 & 16 & 146 & 950 & 23 & 8866 \\
0.9\(\times\) & 1147 & 187 & 15 & 134 & 812 & 21 & 8405 \\
0.75\(\times\) & 941 & 174 & 13 & 134 & 621 & 21 & 8405 \\
0.5\(\times\) & 593 & 138 & 9 & 131 & 315 & 20 & 8345 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Summary of margin variations’ results. The gross profit, total costs, and net profit are presented in thousands of USD per week. The letter \(\times\) represents the margin’s initial value. (i) better margins in comparison with those of the middlemen, (ii) technical assistance and farm inputs, and (iii) on-the-spot cash payments. The E-choupal initiative [11] is an example of success in the transformation of rural India with these three ideas. Third, increasing the capacity of the hubs does increase the net profits, but there can be limitations. Although the fixed costs and transportation costs also increase, the larger quantities that these hubs can handle result in greater profits as presented in Section 5. The question is if the hubs' concessionaires can increase their operation capability. As said above, increasing the capacity can be seen as adding days of operation, which seems plausible. A potential limitation for the extended operation is the availability of trucks. For example, a given truck cannot be used on a daily basis and will only be available at the hub in three to five days, depending on the route. Lastly, there are difficulties to overcome before the successful implementation of a model like this: First, middlemen would not easily give up their business. Intermediation in Colombia is a big business, and a big hub competitor would not be welcome.