From Fig. 7 and Table 2, it can be easily observed that in Case-1, the wind speed ratios associated with the southerly winds are somewhat larger than those for the northerly winds at each tunnel. The wind speed ratio from the southerly winds is averaged at 1.90 for tunnel-1, 1.90 for tunnel-2, 2.08 for tunnel-3 and 2.19 for tunnel-4, whereas the mean values related to the northerly winds are 1.72 for tunnel-1, 1.69 for tunnel-2, 1.86 for tunnel-3 and 1.90 for tunnel-3, respectively