Fog is the one condition where the road ahead simply disappears. You can have perfect grip, a warm engine and dry tyres, yet still be in real danger — because you can't see far enough to react to what's coming. That changes how you drive more than almost any other weather.
The trap with fog is that it feels slower and safer than it is. Everything looks still and quiet, so your brain assumes there's time. In reality you might only be able to see a car length or two ahead, which means you have to be able to stop within that gap. If you can't, you're driving faster than your eyes can keep up with.
This guide keeps things simple. Do two things well and you've handled fog: buy yourself distance by slowing down and leaving a bigger gap, and get your lights right so you can see and be seen without dazzling anyone. Everything else is just detail hanging off those two ideas.
Study time
36 min
Level
Advanced
Confidence
+10%
Practice
34 Qs
What you'll be able to do
- Understand why bad weather stretches your stopping distance so much — and the simple rule that keeps you safe in it.
- Understand which lights to use in rain, fog and gloom — and the one fog-light rule that catches people out.
- Understand how to handle the weather that isn't rain — gusts, dazzling sun, and water across the road.
The facts that matter
- Use dipped headlights in fog — never main beam, which reflects off the fog and dazzles you.
- You must be able to stop within the distance you can see to be clear, so slow down and leave a bigger gap.
- Use front and rear fog lights only when visibility drops below about 100 metres.
- Switch fog lights off as visibility improves — they dazzle others and can hide your brake lights.
- Don't follow the tail lights ahead; they give a false sense of security and mean you're too close.
- Fog is often patchy and thicker on high ground or near water, so it can worsen without warning.
Make it stick
Memory anchors
Dipped, not dazzled
Main beam in fog doesn't reach further — it bounces straight back off the water droplets and lights up a white wall in front of you. Dipped beam aims lower and under the fog, so you actually see more. When it's foggy, dip it.
See it, stop in it
Whatever distance you can clearly see, you must be able to stop inside it. If fog cuts your view to fifty metres, your speed has to match a fifty-metre stop. Let your eyes set your speed, not your schedule.
Under 100, fog lights on
Fog lights are for serious fog — visibility below roughly 100 metres, about the length of a football pitch. The moment you can see further than that, switch them off so you don't become the dazzle you were trying to cut through.
Stay sharp
The mistakes everyone makes
Chasing the tail lights in front
It's tempting to lock onto the red lights ahead and let them pull you along — suddenly you can "see" again. But those lights only look close because you've crept up on them, and if that driver brakes hard you have no room. Drop back until you're guiding yourself by the road, not by someone else's bumper.
Leaving fog lights on once it clears
Fog is patchy, so you'll often drive out of it into a clear stretch. Rear fog lights left on are as bright as a brake light — they dazzle the driver behind and mask the moment you actually brake. Switch them off as soon as the fog lifts; it's a legal requirement, not just good manners.
Treating patchy fog as "basically fine"
A clear gap between fog banks fools people into speeding back up, only to hit a thick patch at the wrong speed. Fog collects on higher ground and near water and can close in within seconds. Keep your speed sensible through the clear bits so the next bank isn't a shock.
Out on the road
What this looks like in real life
The junction you can hear before you see
You reach a give-way line in thick fog and the road looks empty — but empty is exactly what you can't trust here. You wind the window down and listen. An engine is building somewhere to your right, so you wait rather than pull out. A sound gave you the warning your eyes couldn't, and a small habit kept you out of the path of a car you never saw coming.
Fog lifting on the dual carriageway
You've spent ten minutes crawling through dense fog with your fog lights on, and then the road opens out and you can see for half a mile. That's your cue to reach for the fog light switch straight away. Leave them blazing now and the driver behind is squinting into your rear fogs, unable to tell when you brake. Lights off, and everyone behind can read you clearly again.
Quick answers
Frequently asked questions
When exactly can I use my fog lights?
Only when visibility falls below about 100 metres — roughly a football pitch in length. That's the level of fog, heavy rain or snow where normal headlights aren't enough. As soon as you can see further than that you must switch them off, because they're bright enough to dazzle other drivers and can hide your brake lights.
Why shouldn't I use full beam in fog?
Because the light reflects straight back off the tiny water droplets in the fog and throws a bright glare into your own eyes, so you actually see less, not more. Dipped headlights sit lower and cut under the fog, giving you a clearer view of the road. In fog, dipped beam is always the right choice.
How much should I slow down in fog?
Enough that you can always stop within the distance you can clearly see. There's no single speed — it depends on how thick the fog is — but the rule is simple: if you couldn't stop in time for something appearing at the edge of your vision, you're going too fast. Leave a much bigger gap to the vehicle ahead as well.
What should I do at junctions in fog?
Slow right down and treat your ears as a second pair of eyes. Wind the window down and listen for traffic you can't yet see, and only pull out when you're sure it's clear. A gentle use of the horn can also help others know you're there if it's badly reduced visibility.
Turn driving in fog into marks
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Revision checklist
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