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Driving in fog: Dangers & safety tips

driving in fog

Foggy weather and driving don’t always mix. The more fog impacts visibility, the harder it is for drivers to see the road, signs, pedestrians, and other objects and vehicles. Whether it is thick or thin, fog can directly threaten the safety of you and your passengers, and it can cause chain reactions with other cars.

Although fog is a temporary weather phenomenon, it is one of the most dangerous to drive in because it disrupts your field of vision and distorts your depth perception of what you see from behind the wheel.

What causes fog and why is it dangerous?

When water vapor condenses, a large amount of water droplets are produced and suspended in the air, causing both thin and thick layers of fog to appear before you. 

It occurs when humidity is high and/or if there is some form of pollution in the air, such as dust or even salt in locations near the ocean. If you live near a lake or body of water, you may have to navigate fog more often, as it forms more in these areas because of the high levels of humidity.

Fog can be hard to navigate for any driver, no matter how experienced, because it literally clouds your visibility on the road. In many cases, driving in fog can be just as dangerous as driving in rain.

Dangers of driving in fog

When it is foggy outside, the density of the air makes it difficult to see road signs, pedestrians, other cars and even things that are right in front of you on the road. Your chances of getting into an accident are much higher when you are unable to navigate properly, and it can seriously affect others on the road.

Car pile-ups have been and continue to be reported nationwide as a result of fog, with some involving as many as 100 cars or more. Such chain reactions are likely to occur because it is so difficult to see through the fog — and with so many cars impacted, injuries and fatalities can become a serious concern. 

Unlike driving in the rain, where accidents are often due to a car brake system’s delayed reaction on wet pavement, accidents happen in fog simply because drivers have trouble seeing what is in front of them.

How does fog affect a driver’s vision?

It’s no secret that fog is hard to see through, but what is it about fog that makes it so challenging to navigate?

Specifically, fog affects a driver in the following ways:

  • Depth perception can be reduced due to the thickness of the fog.

  • The low contrast caused by fog makes it difficult to distinguish between light and dark areas and objects on the road.

  • Your vision fixates on what is close by due to something called the Mandelbaum Effect, an effect that causes your vision to rest at a distance of only three feet when visibility is weakened. (Normally the human eye can see much further — one study determined that without obstructions, the eye can identify a candle flame from up to 1.6 miles away).

SEE RELATED: The importance of healthy vision for road safety 

Should you use headlights in fog?

When driving in fog, you should use your low-beam headlights. This is the best way to enhance visibility on the road and make your vehicle easier for other drivers to spot.

Always avoid high beams in fog. High beams, or “brights,” cause light to reflect off the road in normal conditions, and during foggy weather, the light can actually reflect off the water droplets in the fog. This may cause glare that can block your view of the road and harm other drivers’ vision even more severely.

Low beams vs. fog lights

Are fog lights the same as low beam headlights? Not quite. Low beam headlights provide aid to seeing things straight ahead of you, while fog lights are designed to point down towards the pavement and illuminate the ground underneath fog to help reduce light reflection. 

Many cars have fog lights as a supplemental feature, but it is becoming more and more common for cars to be designed without them, as they can be ineffective at illuminating your car for other drivers to see you. Fog lights are also more useful for extremely slow speeds, which is not always feasible when you are driving on busy streets and highways.

Tips for driving in fog

If you can’t avoid driving in fog, there are some things you can do to increase your safety on the road. This includes:

  • Give yourself additional travel time to navigate the fog on the way to your destination.

  • Use your low-beam (regular) headlights to help you see better and to help other drivers see you.

  • Make sure there is plenty of room between you and the car in front of you. Reaction times can be delayed in foggy conditions.

  • Follow the lines of the road with your eyes to ensure you are staying within your lane.

  • Avoid distractions such as your cell phone, turning the radio dial, and eating or drinking.

  • If the fog becomes too dense, pull over to a safe area and stop driving until the fog lightens.

SEE RELATED: Night driving tips

Check your vision for road safety

It’s clear that fog can disrupt your field of vision on the road, but driving with blurry vision can add to the difficulty in any weather condition. 

Get your vision checked in a comprehensive eye exam once a year by an eye doctor to make sure your prescription is up to date and that you are seeing as sharply as possible behind the wheel.

READ MORE: The complete guide to road-ready vision

Fog. National Geographic. Accessed August 2021.

At least 40 vehicles crash in dense fog on Highway 198. The Fresno Bee. February 2017.

Weather and accidents: Rain & fog. Green, Marc. Accessed August 2021.

Why fog lamps are starting to disappear. Cobb, James. The New York Times. June 2017. 

At what distance can the human eye detect a candle flame? Krisciunas, Kevin and Carona, Don, Texas A&M University Department of Physics and Astronomy. January 2015.

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