The trap
Many learners think: During heavy rain showers you may switch on your rear fog light, just like in fog, to be more visible to following traffic.
The rule is: You may not switch on the rear fog light in rain, not even during heavy rain showers: the bright red light and its reflection actually hinder following traffic. The rear fog light is reserved for very dense fog or heavy snowfall (visibility <50 m)
Challenge
In heavy rain, many drivers think: 'just as little visibility as in fog, so I can use the same light.' The CBR exam designer tests exactly that equivalence. The book treats the rear fog light for rain and for fog oppositely: in rain it is never allowed, in very dense fog or heavy snowfall it is, under 50 metres of visibility.
Read this section on its own page: Challenge: Fog-light rule: rain versus fog
The model
In rain: dipped beam always, front fog light may be used with seriously impaired visibility (<200 m), rear fog light NEVER (Book p.187-188) — not even in heavy showers. In very dense fog or heavy snowfall: front fog light may be used (<200 m) AND rear fog light may be used (<50 m), but only for as long as it serves your safety (Book p.191).
Read this section on its own page: The model: Fog-light rule: rain versus fog
Core
In (heavy) rain you see less well and the road surface is more slippery (Book p.187). Always switch on your dipped beam in rain. In heavy rain that seriously impairs visibility, you may additionally switch on the front fog light — that is a 'may', not a 'must' for every rain shower. However, you may never switch on the rear fog light in rain, not even during heavy rain showers (Book p.188). The bright red light and its reflection off wet air actually hinder following traffic instead of helping. In weather conditions that seriously impair visibility — visibility less than about 200 metres, whether from rain, snowfall or fog — you may switch on the front fog light (Book p.191). The rear fog light is stricter: that is only allowed when visibility is less than 50 metres due to very dense fog or heavy snowfall, never due to rain. And even then: only use it for as long as it serves safety. Once following traffic has already seen you, the bright rear fog light actually hinders them.
Read this section on its own page: Core: Fog-light rule: rain versus fog
Why it matters
A rear fog light wrongly left on in rain blinds following traffic at exactly the moment the road surface is already slippery and stopping distances are longer — a self-created danger. Conversely, someone who leaves the rear fog light off in truly dense fog is almost invisible to following traffic until they are nearly on top of you. Two opposite risks, one rule that prevents both.
Read this section on its own page: Why it matters: Fog-light rule: rain versus fog
Active recall
You are driving through a heavy rain shower on the road to the ferry terminal in Breskens. Visibility is poor, the road surface is mirror-slick from the water. May you switch on your rear fog light now?
Read this section on its own page: Active recall: Fog-light rule: rain versus fog
Teach back
Explain: what is the difference between the fog-light rules for rain and for very dense fog/snowfall, and why may the rear fog light never be on in rain?
Read this section on its own page: Teach back: Fog-light rule: rain versus fog
Source: RVV 1990 art. 32 · checked 2026-10-22
Frequently asked questions
‘During heavy rain showers you may switch on your rear fog light, just like in fog, to be more visible to following traffic’ – is that true?
No. You may not switch on the rear fog light in rain, not even during heavy rain showers: the bright red light and its reflection actually hinder following traffic. The rear fog light is reserved for very dense fog or heavy snowfall (visibility <50 m)
‘As soon as it rains, you are required to switch on your front fog light, just like your dipped beam’ – is that true?
No. Dipped beam is always mandatory in rain; the front fog light may only be switched on during heavy rain that seriously impairs visibility (visibility less than about 200 m). In ordinary light rain the front fog light is not required
‘Once your rear fog light is on, you keep it on until the fog is completely gone, even once following traffic has long since noticed you’ – is that true?
No. Only use the rear fog light if it improves safety; if following traffic has already seen you, the bright rear fog light actually hinders them. 'Keep it on until the fog is gone' is not a book rule
‘Your rear fog light keeps a following driver at a distance; switch it off and he will immediately drive closer again’ – is that true?
No. Only switch on the rear fog light when it is better for safety; if following drivers have already seen you, the bright light is a nuisance to them