Lesson
Safety margins
Safety margins are about the space you leave around your car — and how much more you need when conditions get worse.
Key rules to know
- Typical stopping distances on a dry road: 12m at 20mph, 23m at 30mph, 36m at 40mph, 53m at 50mph, 73m at 60mph and 96m at 70mph.
- Stopping distance = thinking distance + braking distance. Tiredness, distraction or alcohol increase thinking distance.
- Leave at least a two-second gap in good conditions. Double it in the wet. In icy conditions, braking distances can be up to ten times longer.
- In fog, use dipped headlights. Use fog lights when visibility is seriously reduced (generally below 100m) and switch them off when it improves.
How it applies on the road
Heavy rain on a dual carriageway
Your tyres have less grip and spray hides hazards. Leave at least a four-second gap and slow down.
Steering feels light in standing water
This may be aquaplaning. Ease off the accelerator gently and do not brake or steer sharply.
Common mistakes
- Using the two-second rule in the wet or ice.
- Forgetting that stopping distances roughly double from 30mph to 50mph, even though speed has not doubled.
Official sources
Content written and reviewed by Rob Cordina. Last reviewed: October 2026. Our practice questions are original, written from the Highway Code — they are not official DVSA questions. Always check the latest Highway Code.