Driving in floods and heavy rain
Flooding can happen any time thanks to rain, blocked drains, burst water mains, tides and burst river banks.
You’ll probably hear warnings of sea or river-related flooding from the Environment Agency, or on the news, but surface water flooding from heavy rain or drains that can’t cope is harder to predict and can be very localised.
If you hear there’s flooding on the way, move your car to higher ground to stop it getting damaged. Water plays havoc with electrics and can even cause airbags to go off suddenly some time later.
What should I do when I'm driving in heavy rain?
- Turn your headlights on – the Highway Code says you must use them when visibility is seriously reduced (less than 100m).
- Use fog lights if you like, but switch them off when visibility improves.
- Leave twice as much space between you and the car in front – it takes longer to stop in the wet. If your steering feels light due to aquaplaning, ease off the accelerator and slow down gradually.
- If you break down don’t prop the bonnet open while you wait. Rain-soaked electrics can make it harder to start the engine.
How to stay safe when driving through floods
- Try to avoid standing water if you can.
- Don’t drive into flood water that’s moving or more than 10cm (4 inches) deep. Let approaching cars pass first.
- Drive slowly and steadily so you don’t make a bow wave.
- Test your brakes as soon as you can afterwards.
- Fast-moving water is very powerful – take care or your car could be swept away.
- If you do get stuck in flood water, it’s usually best to wait in the car and call for help rather than try to get out.
Why do I have to slow down when driving through floods?
Driving fast through water is dangerous, inconsiderate and can end up being very expensive.
Your tyres can lose contact with the road, causing you to lose steering control – called aquaplaning. If you feel it happening, hold the steering lightly and lift off to slow down gently until your tyres grip again.
At anything above a slow crawl you’ll throw water onto pavements, soaking pedestrians or cyclists. You could be fined and get points on your licence for this.
It only takes an egg cupful of water to be sucked into your engine to wreck it, and on many cars the engine’s air intake is low down at the front.
What should I look out for when driving in the rain?
- Look out for slip and trip hazards like kerbs under the water.
- Manhole covers can get lifted and moved.
- Water levels can change quickly.
- Assume that flood water is contaminated:
- Urban flood water can carry dangerous bacteria from drains and sewers that could cause disease.
- Rural flood water is more likely to be contaminated by agricultural chemicals and animal waste.
What to look out for when driving in floodwater
- Most drowning deaths happen within only 3m of a safe point.
- Two thirds of those who die in flood-related accidents are good swimmers.
- A third (32%) of flood-related deaths are in vehicles.
- Cold water reduces your muscle strength – 20 minutes in water at 12C lowers muscle temperature from 37ºC to 27ºC, reducing strength by 30%.
- Just 15cm of fast-flowing water can knock you off your feet and be enough for you not to be able to regain your footing.
- It’s a challenge to stand in waist-deep water flowing at only 1m/s. By 1.8m/s (4mph) everyone is washed off their feet.
- If the speed of the flood water doubles, the force it exerts on you or your car goes up four times.
- Just 60cm of standing water will float your car.
- Just 30cm of flowing water could be enough to move your car.
- A mere egg cupful of water could be enough to wreck an engine.
- Flood water can be contaminated and carry diseases.
- Culverts (tunnels carrying water under a road) are dangerous when flooded – the siphon effect can drag in pets, children and even fully grown adults.