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How Hydroplaning Works

What to Do When Hydroplaning

Even if all precautions fail and you do wind up hydroplaning, stay calm. If you keep your head and don't panic, the situation is manageable. First of all, don't slam on the brakes, and don't oversteer. Hold the steering wheel firmly, and keep the nose of vehicle pointed straight ahead. Steer just enough to keep the car going forward. Take your foot off of the accelerator, letting the vehicle slow down on its own.

Before you find yourself sliding across the highway on a cushion of water, find out if your vehicle has regular or anti-lock brakes. Look in the owner's manual, or ask your mechanic. If you start to hydroplane and you must brake to avoid a collision, pump regular brakes rapidly and lightly. Brake in a normal fashion for anti-lock brakes --but don't brake too hard. The vehicle's computer will mimic the pumping action for you. If your vehicle's tires have any contact with the road at all, you should begin to slow and regain control.

The Internet is full of dire warnings about not using cruise control in a rainstorm. These tales tell of accidents in which the cruise control sensed a hydroplaning situation and actually caused the vehicle to accelerate. Although there's no evidence for that, most experts do advise that cruise control not be used in rainy weather. If you do hydroplane, you would have hit the brakes to disarm it, and you don't want to brake unless it's absolutely necessary.

Highway engineers have been working on the dilemma of hydroplaning since the 1960s, when higher speeds and the wider interstate highways both led to a higher number of accidents. Prevention of hydroplaning through highway design is governed by the choice of materials and the building specifications, particularly something called cross slope -- the direction perpendicular to that of that main slope. If built correctly, water will be able to drain easily from the roadway. Grade is also important in preventing hydroplaning, since water drains better on a steeper grade, and vehicles going uphill are less likely to hydroplane.

In addition to finding better building techniques, road builders are also working with new materials that lower the odds of hydroplaning. Texturing the roads with grooves can help reduce the probability of hydroplaning, but only concrete roads can be grooved, or tined. Most highways are built with a cheaper, hot mix asphalt, which can't be grooved. It's also more prone to rutting, which contributes to hydroplaning.

For lots more information on cars and road safety, see the links on the next page.