On October 21, 2007, the vehicle accident to which the windshield was damaged by wave action occurred on a coastal road along the Japan Sea. In this study, the situation when the accident occurred was clarified by the hearing such as those who drove and the road administrator. Wave overtopping rate and vertical wave force acting on the vehicle were reproduced by two dimensional hydraulic model tests with irregular waves. The hydrodynamic pressure that acted on the windshield was formulated by using the speed of the vehicle. The hydrodynamic pressure is proportional to the second power of the speed of the vehicle, and the influence of the angle of the windshield became clear. The limitation of the speed of the vehicle is also proposed to evade the vehicle damage.