Rain and hydroplaning — North Carolina Permit Test

In rain you must use your headlights and windshield wipers, drive more slowly, and allow at least twice the normal following distance, because stopping distances on slippery pavement are two to 10 times longer.

Wet brakes and wet tires stop a car far more slowly. The extra following distance is where that slowness gets absorbed.

Stopping distances on slippery pavement increases from two to 10 times farther than on dry pavement; therefore, slow down and allow yourself at least twice the normal following distance.

Roads are most dangerous in the first 10 to 15 minutes of rain, when water mixes with oil, dust and rubber into a slick film; drive at least five to 10 mph slower on wet pavement.

A road that has been dry for days is coated in oil. The first rain floats it, and the first minutes are the slickest.

For the first 10 to 15 minutes, rain combines with oil from asphalt and vehicles, and with dirt, dust and rubber to create a slick surface.

Hydroplaning happens when a thin sheet of water lifts the tires off the road; it can start at speeds as low as 30 mph in water little more than 1/8 inch deep.

It does not take a flood. A film of water and a modest speed are enough to lift the tires and leave you steering nothing.

Hydroplaning can start at speeds as low as 30 miles per hour and in water little more than 1/8 inch deep.

If you begin to hydroplane, take your foot off the gas, resist using the brakes, keep the steering wheel straight, and let the car slow until the tires grip again.

Tires riding on water cannot brake or steer. Every input you make is stored up for the moment they touch down.

If you do begin to hydroplane, take your foot off the gas pedal. Resist your instinct to use the brakes. Keep your steering wheel straight and let the car’s momentum decrease until the tires grip the road again and you regain control.

Never use cruise control in the rain or after it has rained, because the time it takes to switch it off when the car hydroplanes can cost you control.

Cruise control keeps the power on while the tires are floating. The seconds spent canceling it are the seconds you needed.

Never use cruise control when it is raining or after it has been raining.

Warning signs of standing water that can cause hydroplaning include reflections on the road surface, dimples made by raindrops, a slushing sound from the tires and a loose feeling in the steering.

The car tells you before it lets go. The sound and the light steering are the warning to slow down.

These include visible reflections on the surface of the water; “dimples” created by rain drops as they hit the water; a “slushing” sound made by your tires; and a “loose” feeling in your steering wheel.

Tires with deep, open treads let water escape and help prevent hydroplaning; worn or underinflated tires grip less, and for handling skids tire pressure should be on the high side of the manufacturer’s range.

A firm tire keeps its shape and its grooves. A soft one flattens, closes its channels, and floats sooner.

To properly handle skids, it is better to have tire pressure on the high side, rather than the low side, of the manufacturer’s specifications.

Direct or reflected sunlight is dangerous; adjust your visor and wear sunglasses, and if that does not help, stop at the roadside until you can drive safely.

A blinding glare takes the road away as surely as fog. If the visor and glasses fail, the only safe speed is zero.

To reduce this problem, adjust your sun visor and wear sunglasses. If these do not help, stop on the roadside until you can drive safely.

How much following distance should you allow in rain?

At least twice the normal distance. Wet brakes and wet tires stop a car far more slowly. The extra following distance is where that slowness gets absorbed. North Carolina Driver Handbook, p.72: “Stopping distances on slippery pavement increases from two to 10 times farther than on dry pavement; therefore, slow down and allow yourself at least twice the normal following distance.”