The models are run on a set of generated instances, and the experimental results are shown in Table 1 and 2 respectively. The problem size is defined by the number of post boxes. According to the results in Table 1 and 2, the optimal routings from both models are different since the first model considers the real distance, but the time travelled the second model depends on the possible velocity of vehicle of each route. It is found that when one vehicle is used for collecting letters, LINGO can easily find optimal solution in the small size problems (5-25 post boxes), however the computational time increases when the number of post boxes increases.