|On October 21、 2007、 an accident occurred in which a vehicle’s windshield was damaged by wave action on a coastal road along the Sea of Japan. In this study、 the conditions of the accident were clarified through interviews with parties involved such as the vehicle’s driver and the relevant road administrator. The wave overtopping rate and the vertical wave force acting on the vehicle were reproduced through two-dimensional hydraulic model tests with irregular waves、 and the hydrodynamic pressure acting on the windshield was expressed by a formula from the speed of the vehicle. The hydrodynamic pressure was found to be proportional to the second power of the vehicle’s speed、 and the influence of the windshield angle was clarified. As a result、 the limitation of vehicle speeds is proposed as a way of avoiding this type of vehicle damage.