When the road is wet (there is a water layer on the road surface), the road marks become blurred and drivers are distracted. We discuss the contributing processes and identify which processes are dominant to the occurrence of this phenomenon. Modelling and a simple experiment demonstrate that the dominant processes are: (a) refraction of light by the water layer that reduces the beam angle of the light that enters the driver's eyes, (b) reflection of light in the water layer, and (c) the glare.