In this study it is intended to review the moving characteristics of smoke by performing visualization for calculation of the optimal smoke exhaust air volume in case a fire occurs in tunnels where transverse ventilation is applied, and to obtain basic data necessary for design of the smoke exhaust systems by deriving optimal smoke exhaust operational conditions under various conditions. As a result of this study, if it was assumed 0 critical velocity in the tunnel, the smoke exhaust air volume was limited within 250 meter in the road-tunnel disaster prevention indicator and the exhaust efficiency was from 55.1% to 95.8% in the result of this study. In case of oversized exhaust ports, the generated smoke is more than the case of uniform exhaust. When the critical velocity in the tunnel is 1.75 m/s and 2.5 m/s, the optimal smoke exhaust air volume has to be more than $173;m^3/s$, $236;m^3/s$ for the distance of the moving smoke which can limit the distance to 250 m.