The present study deals with the control of leakage of pollutants from exit portals of road tunnels. This report, supplementing the 1st report, describes an accuracy of the theoretical formula for concentration distribution and leakage ratio of the ventilation method, consisting of a transverse ventilation system with an extraction shaft. The results of this study confirm the effectiveness, both in theoretical and experimental terms, of the present ventilation method as a measure against environmental pollution around exit portals of road tunnels.