Hydroplaning
Hydroplaning occurs when the drainage capacity of the tire tread pattern and the pavement surface is exceeded; water builds up in front of the tire and creates a water wedge which can lift the tire off the pavement, thus reducing the tire/pavement friction to zero. Hydroplaning is a function of the water depth, roadway geometrics, vehicle speed, tread depth, tire inflation pressure, and conditions of the pavement surface, so it is difficult to calculate the exact conditions where hydroplaning will occur. The potential for hydroplaning increases as the depth of water over the roadway increases. Hydroplaning can occur at 55 mph with as little as 0.08 inches (2mm) of water.
Because the factors that influence hydroplaning are generally beyond the designer's control, hydroplaning is impossible to prevent. However, the physical characteristics that may influence hydroplaning can be minimized with the following considerations:
- Proper transverse slopes reduce the amount of water flowing over the pavement and prevent excessive ponding. The longitudinal slope is somewhat less influential in decreasing the potential for hydroplaning.
- Conscientious placement of inlets reduces or eliminates water flowing over the pavement and reduces excessive ponding. Transverse drains should not be used without serious consideration for small wheeled vehicles.
- Permeable surface courses and high macrotexture surface courses influence both water film thickness and the interaction of tires with the water film.
- Grooving may be a corrective measure for severe localized hydroplaning problems. Transverse grooving (perpendicular to the direction of traffic) produces better results that longitudinal grooving (parallel to the direction of traffic). In addition, longitudinal grooving has the potential to retard flow off the roadway.
The potential for hydroplaning can be evaluated using an empirical equation based on studies conducted for the FHWA publication “Bridge Deck Drainage Guidelines” (
).