Warning signs
Tunnel ahead
What it means
A tunnel is coming up and the light will drop sharply as you go in. Take your sunglasses off before you enter, switch on dipped headlights, and leave a bigger gap than usual. Your eyes need a moment to adjust, so you may not pick up brake lights in front of you straight away.
Highway Code Rule 126 — read it on GOV.UK
More on signs like this: Warning road signs explained: junctions, bends, narrowing roads and hazards
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Sign images: Department for Transport, © Crown copyright. Used under the Open Government Licence v3.0.