Snow and ice removal also decreases road slipperiness; snowploughs and snow blowers can remove the snow from the road surface while gritters drop road salt and sand, which both melts the snow and ice from the road surface, and provide a rougher surface to grip onto. However, in dry conditions, sand and salt on the road surface can themselves increase road slipperiness and pose a danger to road traffic, and therefore, roads are cleared by street sweepers after roadworks and gritting to make sure that all the loose material is cleared from the road surface.