Fog changes a familiar road in minutes.
Landmarks disappear, distances become hard to judge, and the car ahead can vanish into a gray wall even at a moderate speed.
The National Weather Service notes that fog, particularly when dense, can be hazardous to drivers and contributes to numerous travel accidents every year.
This guide explains how fog fools your eyes, what the official safety tips say and how to decide when it is time to stop driving altogether.
Why fog is so hard to drive in
Fog is essentially a cloud sitting at ground level, made of tiny water droplets hanging in the air.
Those droplets scatter light in every direction, which lowers contrast and blurs the edges of everything you look at.
Your eyes simply have less information to work with.
Cars, pedestrians and the edge of the road appear later than you expect, and they can seem farther away than they really are.
Fog is also patchy.
A road can be clear for a mile and then drop into a dense bank in a low spot, near a river or lake, or just over the top of a hill.
That sudden change is where many multi-car crashes begin.
One driver brakes hard on entering the fog, while the drivers behind are still moving at clear-weather speed.
Slow down and give yourself time
The first tip on the National Weather Service fog driving page is to slow down and allow extra time to reach your destination.
A practical way to think about speed in fog is that you should always be able to stop within the distance you can see.
If the road fades out a short way ahead, keep slowing until you could brake to a stop inside that clear zone.
Leaving early takes the pressure off.
When you are not racing the clock, it is much easier to hold a slow, steady pace and let faster drivers go.
Use low beams, never high beams
Lighting is where many drivers go wrong.
The NWS advises making your vehicle visible both ahead of you and behind you by using your low-beam headlights, since that means your taillights will also be on. Use fog lights if you have them.
The same guidance is blunt about high beams: never use them in fog.
High-beam light bounces off the water droplets and creates glare, making it harder for you to see what is ahead of you on the road.
Daytime running lights are not enough on their own.
On many vehicles they light only the front of the car and leave the taillights dark, so switch the headlights on yourself instead of trusting an automatic setting.
Fog lights, on cars that have them, are mounted low and aimed at the road surface beneath the fog.
Turn them off once visibility improves, because in clear air they can dazzle other drivers.
Leave much more following distance
The NWS recommends leaving plenty of distance between you and the vehicle in front of you to account for sudden stops or changes in the traffic pattern.
In fog, the driver ahead may brake for something you cannot see yet.
A longer gap gives you time to react smoothly instead of slamming on the brakes, which also protects you from the driver behind you.
Resist the urge to tuck in close behind another car just because its taillights help you find the road.
If that driver stops suddenly or drifts off the pavement, you will follow them straight into trouble.
Follow the lines on the road
To stay in the proper lane, the NWS suggests following the lines on the road with your eyes.
The painted edge line on the right is especially useful because it keeps you away from oncoming traffic.
Keep the glass clear so you can actually see those lines.
Run the defroster and wipers as needed, since fog droplets collect on the windshield, and turn down the radio and put the phone away so all your attention stays on the road.
Opening a window slightly can help you hear traffic you cannot see yet, especially at intersections and railroad crossings.
When to pull over
Sometimes fog becomes so thick that there is no safe way to keep going.
In extremely dense fog where visibility is near zero, the NWS says the best course of action is to first turn on your hazard lights, then pull into a safe location such as the parking lot of a local business and stop.
If there is no parking lot or driveway to pull into, the guidance is to pull the vehicle off to the side of the road as far as possible.
Once you have stopped:
- Turn off all lights except your hazard flashers.
- Set the emergency brake.
- Take your foot off the brake pedal so the taillights are not lit.
That last step can feel strange, but it matters.
Drivers in fog tend to steer toward the lights in front of them, and a car on the shoulder with glowing brake lights can look like a car still moving in the lane.
Showing only the hazard lights tells other drivers you are stopped and out of the way, so they do not mistakenly run into you.
Wait until visibility improves before pulling back onto the road, and merge carefully when you do.
Plan ahead on foggy mornings
Fog is often thickest in the early morning and late at night, and it frequently thins out as the day warms.
If your schedule allows, a short delay can turn a stressful drive into an easy one.
- Check the local forecast before you leave and look for dense fog advisories.
- Learn the stretches of your route that fog up first, such as valleys, bridges and roads near water.
- Clean the inside and outside of the windshield and replace worn wiper blades before fog season.
- Make sure every headlight, taillight and fog light works.
Common fog driving mistakes
- Switching on high beams, which only adds glare.
- Relying on daytime running lights that leave the taillights off.
- Following another car closely to use its taillights as a guide.
- Braking hard when entering a fog bank instead of slowing early and gradually.
- Stopping in a travel lane, or stopping on the shoulder with the brake lights still on.
The bottom line
Driving in fog comes down to two goals: see as much as you can, and make sure everyone else can see you.
Slow down, use low beams, leave a long gap and follow the edge line.
When the fog is too thick for any of that to work, do not push on.
Turn on your hazards, get off the road in a safe place and wait it out.
Sources and Further Reading
- National Weather Service: Driving in Fog — supports the guidance on slowing down, low-beam headlights and fog lights, never using high beams, following distance, following the road lines and what to do in near-zero visibility.
- National Weather Service: Fog Safety Overview — supports the statement that dense fog is hazardous to drivers and contributes to numerous travel accidents every year.