Final answer:
Hard surface roads are likely to be especially slick when it's raining lightly due to oily residue, when it's raining heavily, during snowy or icy conditions, or when the pavement is new. Road salt and the right tires help increase friction and improve traction 1) It is raining heavily.
Step-by-step explanation:
Hard surface roads are likely to be especially slick when there is ice or snow on the road, it is raining heavily, the road is newly paved, or when oil and gasoline have leaked onto the surface. Specifically, when light rain falls onto a road with leaked oil and gasoline, it can cause the road to become very slippery, making it harder for tires to maintain a good grip and consequently reducing the control of the car.
A heavy rain may wash away some of these substances, offering better control than during a light rain. In cold regions, the application of salt on the roads helps to lower the freezing point of water, thereby melting the snow and ice and reducing slick conditions. When considering tire selection for an icy road, you want to have tires that create more friction, much like winter tires that provide better traction than summer tires under such conditions.