Analysis of the critical thickness of water film for driving on road surface in rainy condition

Hydroplaning occurs when vehicles drive in rainy days. It is analyzed that the wheel forces with the water, furthermore, the conception of critical thickness of water film is brought forward, and the formula for calculating the critical thickness of water film on the pavement is derivative based on momentum theorem. Finally, the values of critical thickness of water film for different driving speeds are given, and it is proved that the formula is reliable by contrasting with the values from other experiential formula. The result affords calculating method for the control of safety problem of driving on road surface in rainy days.