This research mainly uses the image binaryzation to quantify water fog in order to have a better understanding about the water fog degree that drainage pavement reduces and the relationship between drainage pavement thickness and water fog. By observing the water fog that tires splash while raining, the study result shows that the most adequate pavement thickness of drainage pavement is 4cm. The water fog it reduces is double of 2.5cm drainage pavement. The thicker drainage pavement is also considered safer to drivers. About the drainage path, the shorter the faster it can drain off the rainwater and reduces the water fog degree that heavy vehicles splash.