Driving in Heavy Rain and Avoiding Aquaplaning

What heavy rain changes

Rain affects driving in three ways. It reduces grip between the tires and the road, it makes it harder to see, and it makes other drivers’ behavior less predictable. The first rain after a dry spell can be especially slippery, because water mixes with oil and dust on the road surface. Heavy rain adds a fourth problem: standing water, which brings the risk of aquaplaning, sometimes called hydroplaning in North America.

What aquaplaning is

Tires are designed to push water out of the way through their tread grooves. When there is more water than the tread can clear at the speed you are traveling, a wedge of water builds up under the tire and lifts it away from the road surface. For a moment, the tire is riding on water instead of gripping the road.

When this happens, you lose much of your ability to steer, brake and accelerate. The car may feel suddenly light, the steering may go slack, or the engine may rev without the car speeding up. It often lasts only a short time, but it can be frightening.

Aquaplaning becomes more likely when:

• speed is high, because tires have less time to clear water
• tread is worn, because there is less channel space
• tire pressure is too low, which changes the shape of the contact patch
• the water is deep, for example in wheel ruts, dips and the outside lanes of highways where water collects
• the rain is heavy or has just begun

How to reduce the risk

Slow down. This is the single most useful step. A lower speed gives the tires more time to disperse water, and it gives you more time to react. There is no universal speed at which aquaplaning begins, so the safest approach is to reduce speed as the rain gets heavier.

Look after your tires. Check tire pressure regularly, and use the pressure shown in your owner’s manual or on the door-jamb label. Check tread depth too, because tires close to the legal minimum cope poorly with water. Some drivers replace tires earlier for this reason. Local legal minimums differ, so check yours.

Avoid standing water. Where you can safely do so, drive in the tracks left by vehicles ahead, avoid ruts and puddles, and stay clear of the road edge where water pools. Be careful not to make sudden changes to avoid a puddle.

Be smooth. Gentle steering, braking and acceleration keep the tires working within the grip they have. Smooth driving is good practice in all weather, and it matters more on wet roads.

Keep your distance. Wet roads can lengthen stopping distances significantly. Allow a longer following distance, often at least double what you would use on a dry road, and more in heavy rain.

What to do if you aquaplane

1. Stay calm. Panic leads to sudden inputs that make things worse.
2. Ease off the accelerator. Do not brake hard or turn the wheel sharply.
3. Hold the steering straight. Keep it pointing where you want to go, with small corrections if needed.
4. Wait for the tires to regain grip. You will usually feel the steering weight return.
5. Brake gently once grip returns. If the car has anti-lock brakes, firm braking may be appropriate and the system will pulse; follow your manual’s guidance.

If the car skids once grip returns, steer gently in the direction you want to go. It is a good idea to slow down afterward and decide whether to continue or find a safe place to wait out the heaviest rain.

Visibility in heavy rain

• Use low-beam headlights, and automatic wipers if you have them, in rain. Many places require headlights when wipers are in use; check your local rules.
• Replace worn wiper blades. Streaking is a clear sign, and it is an inexpensive fix.
• Keep the washer reservoir filled. Spray from trucks can cover your windshield in seconds.
• Use the defroster and air conditioning to prevent the inside of the glass from fogging. Defrosting windows works the same way whether the problem is cold or damp.
• Give large vehicles extra space. Their spray reduces your view, and passing them in heavy rain can be unpleasant.
• Do not use hazard lights while driving unless local law says it is acceptable.

If rain becomes so heavy that you can barely see the road, it is better to pull off safely and wait than to continue. Avoid stopping under bridges or trees, where you might block traffic or be at risk.

Deep water and flooding

Standing water may be deeper than it looks. If you meet water that covers the road, the section on flooded roads is important: turning around is usually the safest choice. Driving through even moderate depth can stall an engine or cause other damage.

Cruise control and rain

Cruise control can cause problems in heavy rain because it keeps applying power when the tires begin to aquaplane. Many drivers prefer to turn it off in wet conditions so they stay in direct control of the speed. Check your owner’s manual for guidance on adaptive systems and traction control in rain.

After the storm

Brakes can feel weaker after driving through a lot of water. Test them gently once you are on a clear road. Look at your tires for damage, and let the interior dry if floor mats got wet, to avoid musty smells and fogging.