Abstract: Accidents may occur in highway tunnels when the road surface is damp and slippery. The mechanisms for the damp and slippery road surfaces in tunnels are analyzed on basis of meteorological observations and hydrogeological analysis. It is concluded that the main cause for such phenomenon is the dew produced when moist and hot air outside the tunnel entering the tunnel. Finally, countermeasures are proposed. 

Key words: Baojiashan tunnel, damp and slippery road surface, damp recovery 