In a milk-run operation, which is utilized widely in auto manufacturing industry, each
pickup truck makes sequential stops at auto parts suppliers to collect supplies and
then delivers them to the assembly plan. Figure 2 depicts a simplified diagram of the
operation.
Figure 2. Milk-run supply procurement system
The milk-run system can improve cargo loading efficiency because trucks from the
assembly plant make the rounds to collect small number of parts from each supplier
on the route only when needed, thus increasing cargo space utilization, lowering the
number of trucks on the road, and cutting CO2 emissions. 4
In this paper, we address the vehicle routing problem in a milk-run network by
combining truck stops sequentially based on their commodity-fleet compatibility,
origins, and destinations in order to find the cost minimizing milk-run plan satisfying
all supplies demanded.
The authors propose a mathematical model representing the problem and two solution
approaches— an ordinary mathematical programming algorithm and a columngeneration-based branch-and-bound algorithm—and test the model using large-scale
problems.