How Hydroplaning Works

Image Gallery: Car Safety Cars spray water in downtown Auckland, New Zealand, as they drive through deep puddles during heavy rain. See more car safety pictures.
Bruno Vincent/Getty Images

You're cruising down the interstate, listening to the morning radio show and thinking about everything you have to do when you arrive at work. The presentation that's due next week is on your mind, along with the fact that you haven't even started on it. Your boss is also breathing down your neck. On top of everything else, it's raining. It's nothing much, but it's enough to keep you from making your daily lunchtime escape to the park. As your mind wanders somewhere else, you drive your car through a deep patch of water. One second you're singing along with the radio, the next you're hurtling out of control into the next lane. Fortunately, traffic's not too heavy. You didn't hit anyone, but the experience shakes you up and, for the moment, clears your mind of your other worries. At a more moderate speed, you make your way to the office, vowing to take driving in the rain more seriously in the future.

You've just undergone the potentially dangerous experience of hydroplaning. Hydroplaning occurs when a sheet of water comes between the vehicle's tire and the pavement. The tire, because of wear or poor drainage on the road, can't move water out of the way fast enough. The rubber doesn't touch the road, the vehicle loses traction and the driver loses control of steering. Some people liken it to sliding on a sheet of ice. Braking or steering can't help, because the vehicle's tires aren't in contact with the road. Hydroplaning can occur with any type of vehicle. The water depth must be over a tenth of an inch (0.3 centimeters) for hydroplaning to occur, and the vehicle's speed needs to be 50 miles per hour (22.35 meters per second) or more.


Hydroplaning is a common cause of accidents, and tire manufacturers are continually coming up with new tread designs that attempt to channel water away and make a path for the tire. Engineers are working on new materials and new highway designs to lessen the chances of hydroplaning.

How Hydroplaning Occurs

A London taxi cab drives through a patch of standing water, risking hydroplaning, after a heavy downpour.
Michael Bradley/Getty Images

To understand how hydroplaning works, you need to know how traction works. Traction is the friction that builds up between the tires on a car and the pavement. Rolling traction is the interaction between the tire and the surface, which results in forward motion. When water coats that surface, the tire can't obtain traction. Hydroplaning occurs when your tires move over a wet surface so quickly that they don't have time to displace enough water and contact the surface. The water lifts the tire up from the surface, and the vehicle begins to hydroplane.

While speed, road conditions and tire wear all play a part, the main cause of hydroplaning is water depth. Hydroplaning is possible whenever water accumulates to a depth of one-tenth of an inch (0.3 centimeters) or more for at least 30 feet (9.14 meters) and a vehicle moves through it at 50 miles per hour (22.35 meters per hour) or more [source: Crash Forensics]. Tire size and tread patterns are also important. Hydroplaning is more likely to happen if your vehicle has narrow tires. Worn tires are more dangerous in wet conditions. Certain tire tread patterns are better at channeling water away than others. All-wheel drive vehicles are more likely to hydroplane than two-wheel drive vehicles, because their computerized differentials may shift power from the front to the rear tires, creating a hydroplaning situation. Heavy vehicles are less prone to hydroplaning.


Regardless of your tires or what type of vehicle you drive, there are a couple of things you can do to prevent hydroplaning. First, slow down. Speed increases the likelihood of hydroplaning. Even if you do hydroplane, going slower will mean you're in less danger. Another tip: Watch the drivers ahead of you. Erratic steering from them could mean you're coming to a dangerous patch. If the cars ahead of you suddenly throw up more water, it may mean that they've run through a puddle that could cause you to hydroplane.

Now, let's figure out what to do if (and when) you find yourself in a hydroplaning situation.


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.


Lots More Information

Related HowStuffWorks Articles

  • Badnews4u. "Sum.hystory4u." (Nov. 18, 2009)
  • Davidson University. "Rolling Friction." (Nov. 12, 2009)
  • Erie Insurance. "What You Need to Know About Hydroplaning." June 8, 2009. (Nov. 12, 2009)
  • Glennon, John C. "Hydroplaning -- The Trouble with Highway Cross Slope." Crash Forensics Motor- Vehicle Accident Investigation and Reconstruction Services. Jan. 2006. (Nov. 16, 2009)
  • Horne, Walter B. and Dreher, Robert C. "Phenomena of Pneumatic Tire Hydroplaning". National Aeronautics and Space Administration. Nov. 1963. (Nov. 12, 2009)
  • Kurtus, Ron. "Prevening Loss of Traction." School for Champions. March 28, 2008. (Nov. 18, 2009)
  • Ong, G.P. and Fwa, T.F. "Modeling of the Hydroplaning Phenomenon." National University of Singapore. Dec. 2005. (Nov. 16, 2009)
  • Smart "Hydroplaning (Aquaplaning)." (Nov. 16, 2009)
  • University of Pittsburgh, "Safety & Security Committee Newsletter." 2007. (Nov. 16, 2009)
  • Walter, J.D., et al, "Frictional Interaction of Tire and Pavement." American Society for Testing and Materials. Feb. 1983. (Nov. 16, 2009)