Fog, Night Driving & Glare

At night and in fog, most of what you react to is assumption, not actual sight. Understand how to adjust your lights, your speed and your eyes to match what you can really see.

Learner's permitAll U.S. states
⏱️ About 12 min

In fog or at night, your eyes aren't lying to you — there just isn't as much light reaching them as you're used to. The fix isn't always "more light." Sometimes more light (like your own high beams in fog) makes things worse. Understand why, and reduced-visibility driving stops being guesswork.

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The big idea: Fog and darkness both shrink how far ahead you can actually see. Match your speed, your beam choice, and where you look to that shrunken distance, rather than to the speed and habits you'd use in daylight.
🎯 By the end, you'll be able to
  • Explain why low beams work better than high beams in fog
  • Define "overdriving your headlights" and adjust your night speed accordingly
  • Use the right edge line as a visual reference when visibility drops
  • React correctly to glare from oncoming headlights or a low sun
📎 Helpful to know first

Fog: why high beams make it worse

Fog is made of countless tiny water droplets suspended in the air near the ground. High beams are aimed up and out, so in fog that light reflects directly off the droplets close to your windshield and bounces back into your eyes — a wall of glare that actually reduces what you can see, similar to driving into the glare of your own headlights.

Low beams aim down and closer to the road, lighting the pavement in front of you without lighting up the droplet layer above it. If your car has front fog lights — mounted low, with a wide, flat beam — use them too; they're built to sit below the worst of the fog.

The solid white line marking the right edge of your own lane.
🔑 Use the edge line, not the taillights ahead
In heavy fog, following another vehicle's taillights and matching its speed isn't a safe strategy — you can't see what's making it slow down or stop. Instead, use the solid white line at the right edge of your own lane (shown above) as a steering reference, slow well below the posted speed, run your low beams, and stretch out your following distance since your own sight distance has shrunk along with the fog.

Night driving: don't overdrive your headlights

A typical car's low beams light the road only a few hundred feet ahead; high beams roughly double that, though the exact range varies by vehicle. "Overdriving your headlights" means traveling fast enough that your stopping distance is longer than the distance your headlights actually let you see — so by the time a hazard comes into view, you may no longer be able to stop before reaching it.

The fix isn't always "switch to high beams." On an unlit road at night, it's often simply slowing down until your stopping distance fits back inside what your headlights actually show you.

✨ Overdriving your headlights, in one line
If your headlights would only show you a hazard after it's too late to stop before reaching it, you're already driving faster than your lights can protect you — slow down until stopping distance and sight distance line up again.

Glare: oncoming headlights and a low sun

When an oncoming car doesn't dim its high beams, or when a low sun sits right at your eye level at dawn or dusk, don't stare at the light source — your eyes will lose their adjustment and leave you briefly unable to see clearly, sometimes for several seconds after the glare passes.

Instead, shift your focus toward the right edge of your own lane — the same edge-line reference from fog driving — and use it to hold your position while the glare passes. Ease off your speed slightly for those few seconds, and keep sunglasses in the car (and use your visor) for low-sun glare.

Check your understanding

1. In fog, you should generally use:
High beams reflect off the water droplets in fog and bounce glare back at you. Low beams aim closer to the road, lighting the pavement without lighting up the fog layer above it.
2. In heavy fog, the safest visual reference to steer by is:
Another vehicle's taillights don't tell you what it's reacting to. The right edge line stays in a fixed, predictable place and helps you hold your lane at a safely reduced speed.
3. "Overdriving your headlights" means:
If a hazard would only appear in your headlights after it's too late to stop, your speed has outrun what your lights can protect you against — the fix is usually to slow down.
4. When an oncoming car's headlights glare into your eyes at night, you should:
Staring into the glare temporarily wrecks your night vision. Looking toward your own lane's right edge keeps you oriented while the glare passes.
🔎 Related lessons
Next: Snow, Ice & Winter Driving Headlights & When to Use High Beams Pavement Markings: Yellow vs White Lines
✅ Key takeaways
  • In fog, use low beams (and fog lights if equipped) — high beams reflect off the droplets and bounce glare back at you.
  • Use the solid white right-edge line as a steering reference in fog rather than following another vehicle's taillights.
  • "Overdriving your headlights" means going faster than your stopping distance fits inside what your lights let you see — slow down at night on unlit roads.
  • When glare hits from an oncoming car or a low sun, look toward your own lane's right edge instead of the light source.
➡️ Fog and darkness hide the road. Snow and ice take away your grip on it — next, how to spot black ice before it spots you, and how much space winter really requires.

Frequently asked questions

Should you use high beams or low beams in fog?
Low beams. High beams reflect off the water droplets that make up fog and bounce the glare back into your eyes, reducing visibility. Low beams (and front fog lights, if your car has them) aim closer to the road instead.
What does "overdriving your headlights" mean?
It means driving fast enough that your stopping distance is longer than the distance your headlights actually let you see — so a hazard could appear too late for you to stop in time. The fix is usually to slow down.
What should you do when an oncoming car's headlights glare into your eyes?
Don't stare at the lights. Shift your focus toward the right edge of your own lane to stay oriented, and ease off your speed slightly until the glare passes.
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Independent educational content — not affiliated with, endorsed by, or connected to any state DMV, the AAMVA, or any government agency. This is study material, not legal advice; always confirm current rules with your state's official driver handbook.