Driving In Heavy Rain
Driving in Heavy Rain and Floodwaters
Driving in wet conditions can be hazardous, but you have a better chance of staying safe if you prepare for wet weather.
Even drivers with local knowledge can be caught out during heavy downpours, as even the most modern road surface is still susceptible to standing water. This creates a potential aquaplaning hazard as well as significantly reducing visibility. Take it easy through standing water and if the steering does become unresponsive due to the rain, ease off the accelerator and slow down gradually.
"If you come across flood water, you should only attempt to drive through if you know it's not too deep and maintain a steady, slow speed to avoid creating a bow wave."
The engine's air intake on many cars is low down at the front of the car and it can take just an egg cupful of water in the combustion chamber to wreck an engine. Water doesn't compress and the piston in effect hits a wall, bending or breaking a con rod. Driving fast - even if the intake's above the water level - could cause water to be ingested
Be safe, and prepare for wet weather:
- Remember that according to the Highway Code: You MUST use headlights when visibility is seriously reduced, generally when you cannot see for more than 100 metres (328 feet). You may also use front or rear fog lights but you MUST switch them off when visibility improves.
Give yourself the best chance of being able to see clearly in wet weather by renewing windscreen wipers if worn or damaged;
- Double the distance you leave between your car and the car in front of you, as stopping distances are increased by wet roads.
- If steering becomes unresponsive due to the rain, ease off the accelerator and slow down gradually.
Floods and standing water
Only drive through water if you know that it's not too deep. Drive slowly and steadily to avoid creating a bow wave. Allow oncoming traffic to pass first and test your brakes as soon as you can after leaving the water.
Don't try driving through fast-moving water, such as at a flooded bridge approach – your car could easily be swept away.
Watch out for standing water, trying to avoid it if you can, and adjust your speed to the conditions.
- Driving fast through standing water is dangerous; tyres lose contact with the road and you lose steering control in what's known as 'aquaplaning'. If you do experience aquaplaning, hold the steering wheel lightly and lift off the throttle until the tyres regain grip.
- Driving fast through standing water is inconsiderate. Driving through water at speeds above a slow crawl can result in water being thrown onto pavements, soaking pedestrians or cyclists. You could face a hefty fine and between three and nine penalty points if the police believe you were driving without reasonable consideration for other road users.
- Driving fast through standing water can cause expensive damage. The air intake on many cars is low down at the front of the engine bay and it only takes a small quantity of water sucked into the engine to cause serious damage. All engines are affected but turbo-charged and diesel engines are most vulnerable.
As you drive slowly through standing water, use a low gear so the engine rev's are higher; water in the exhaust could otherwise damage the catalytic convertor.
If you break down in heavy rain don't prop the bonnet open while you wait for the patrol to arrive.
The engine will be more difficult to start again if the electrics are all rain-soaked.
- The majority of drowning deaths in the UK occur within only 3m of a safe point
- 2/3 of those who die in flood-related accidents are considered to be good swimmers
- 32% of flood-related deaths are by drowning in a vehicle
- After 20 minutes in water at 12C the temperature of the deep muscle of your forearm would drop from 37 ºC to 27ºC, leading to a 30% reduction in muscle strength.
- In water 1m deep (waist high), flows of 1m/s become challenging and by 1.8m/s (4mph) everyone will be washed off their feet.
- If the speed of the flood water doubles the force it exerts on you/your car is quadrupled
- Just six inches of fast flowing water can knock you off your feet and be enough for you to be unable to regain your footing.
- Two feet of standing water will float your car
- Just one foot of flowing water could be enough to move the average family car
- Just an egg cupful of water in the combustion chamber could be enough to wreck an engine
- Flood water can be contaminated and carry diseases
- Culverts are dangerous when flooded – the siphon effect of culverts can drag in pets, children and even fully grown adults