Aquaplaning or hydroplaning by the tires of a road vehicle, aircraft or other wheeled vehicle occurs when a layer of water builds between the wheels of the vehicle and the road surface, leading to a loss of traction that prevents the vehicle from responding to control inputs. If it occurs to all wheels simultaneously, the vehicle becomes, in effect, an uncontrolled sled. Aquaplaning is a different phenomenon from when water on the surface of the roadway merely acts as a lubricant. Traction is diminished on wet pavement even when aquaplaning is not occurring. Causes Every vehicle function that changes direction or speed relies on friction between the tires and the road surface. The grooves of a rubber tire are designed to disperse water from beneath the tire, providing high friction even in wet conditions. Aquaplaning occurs when a tire encounters more water than it can dissipate. Water pressure in front of the wheel forces a wedge of water under the leading edge of the tire, causing it to lift from the road. The tire then skates on a sheet of water with little, if any, direct road contact, and loss of control results. If multiple tires aquaplane, the vehicle may lose directional control and slide until it either collides with an obstacle, or slows enough that one or more tires contact the road again and friction is regained. The risk of aquaplaning increases with the depth of standing water, higher speeds, and the sensitivity of a vehicle to that water depth. Water depth factors Depth of compacted wheel tracks and longitudinal depressions: Heavy vehicles can cause ruts in the pavement over time that allow water to pool. Pavement micro- and macrotexture: Concrete can be preferable to hotmix asphalt because it offers better resistance to rut formation, though this depends on the age of the surface and the construction techniques employed while paving. Concrete also requires special attention to ensure that it has sufficient texture. Pavement cross slope and grade: Cross slope is the extent to which the cross-section of a road resembles an upturned U. Higher cross slopes allow water to drain more easily. Grade is the steepness of the road at a particular point, which affects both drainage and force exerted by the vehicle on the road. Vehicles are less likely to aquaplane while traveling uphill, and far more likely to do so at the trough of two connected