How to drive in heavy rain and flood water

When driving in wet, rainy weather and along flooded roads you will encounter some of the trickiest conditions for motorists to navigate in the UK. Rain, from light showers to heavy downpours, can have a significant impact on visibility, stopping distances and grip while the left over flood water can present its own problems around aquaplaning and even cars getting stuck with flooded engines. If you must drive through heavy rain or flood water, here are our expert tips for staying safe should you encounter the worst.

The first thing you really need to ask yourself is whether your journey is necessary? If you're at home and know bad weather is coming, can your journey wait? If you're at work, is there anything you can do to postpone your trip? With so many communication options available, it might be more viable to work at home, or do anything to help put off driving in bad weather.

Driving in heavy rain

Driving through wet, foggy or imperfect conditions is more about patience and concentration – ensuring you have sufficient time and space to react to events which are happening around you. 

If you’re in a rush to get somewhere because you set off late, a wet road becomes much more of a potential disaster. When you add fog, mist or tyre spray into the equation the risks are trebled, without requiring anyone or anything else to become involved. Checking the weather forecast before you plan to travel could help you factor additional time into your journey, potentially, reducing stress or risks from adverse road conditions.

Check your windows, mirrors and wiper blades

Good vision is key to all safe driving, we know that. But in the wet it becomes even more important because you simply can’t see as well as you can in the dry (no surprises there, Sherlock). It may take you longer to check your mirrors and blind spots properly if your vision is hazy from dirt and grime on the glass. It is also important to check the condition of your wiper blades regularly, as blades with perished or cracked rubber won’t clear your windscreen properly which could also obscure your vision.

Slow down and reduce your speed

The only way you can influence what’s going on around you is to slow down and leave more space between you and other vehicles on the road. If you keep just one mantra in mind, then make it this: only a fool breaks the two second rule. Say it once to maintain a two second gap in the dry; say it twice or more in poor weather.

Stick to this rule and it’ll buy you more time to work out exactly what’s unfolding ahead and, again, enable you to anticipate and avoid bad things well before they actually happen.

Beware of aquaplaning

If it is raining heavily and you’re on a fast road like a dual carriageway or motorway, beware of standing water, as hitting this at speed can lead to aquaplaning. 

Aquaplaning is where a layer of water builds up between the road surface and your tyres, temporarily reducing grip and increasing the risk of the car spinning. If the steering wheel starts to feel light, or your car starts to drift to one side when travelling in a straight line, you may be aquaplaning. 

If you start to aquaplane:

• Don’t brake suddenly, it can make any spinning or sliding worse.
• Reduce acceleration and speed in a controlled manner by taking your foot off the accelerator.
• If you start to spin, turn the steering wheel in the opposite direction to counteract the slide. This should be your last resort

Read our full guide to aquaplaning safety here…

Remember, grip levels are lower

The other thing to remember is that grip levels are reduced in the wet. Tyre technology has come on a long way, and there’s more grip available when cornering than you’d expect – not that you should be pushing that particular envelope on the road. But under brakes, wet grip is a whole different ball game.

Why? Because most of us will at some point have braked very hard indeed in the dry and been utterly amazed by how fast we managed to slow down. The most common scenario is when motorway traffic grinds to a halt right in front of us, seemingly for no reason, and we have to stand on the anchors hard to avoid thumping into the back of the car in front. 

Do the same thing in the wet and it can feel, just for a moment, as if you are accelerating rather than slowing down. That’s because the outright level of grip in the wet really is that much lower than it is in the dry. Yet for most of the time we don’t realise this, because most of us drive well within the limits of what our tyres are capable of, wet or dry. 

In other words, it’s only when things get unpredictable and start to go wrong that we become aware of these limits, and that can happen far quicker and at much lower speeds in the wet than it does in the dry. Hence the need to give yourself as much space and time in which to operate. That applies in all driving conditions, but never more so than when it’s wet.

Driving in floods

Long periods of heavy rain, or rain after a dry spell can result in flooding, especially in low-lying areas and on roads that follow or cross rivers and streams. There are some roads that flood commonly or even ford rivers, and these will feature depth markers at the side of the road to indicate how deep the water is. The basic rule of thumb should be that if you're not sure about how deep a flooded road is, turn around and find an alternative route.

Drive slowly and carefully

Driving through water carelessly could be extremely dangerous. Go too fast, and the bough wave you cause could drench other road users, while the water could find its way into the engine bay. If it then finds its way into the air intake and is ingested by the engine itself, the pistons won't be able to compress the water, causing what's known as hydrolock and engine failure – which will be a costly mistake.

Be sure to avoid crossing fast-flowing flood water. Even shallow water can easily lift up your car and carry it away downstream before you know it. If you don't know its depth, it’s best not to drive through it.

Drive close to the middle of the road

If you need to cross a flooded road, the first thing you should do is approach it in the middle of the road. UK roads are crowned - the highest part is the middle, with the sides set lower to allow rain water to drain off - so the middle of the road will be the shallowest section of the flooded area. Approach at a low speed, but be sure to maintain your speed and continue through without stopping.

Drive through flood water one-by-one

When the flood is severe and you're in a queue of cars, then it's best for each car to pass through one-by-one: the last thing rescue services need is to have to reach more than one car in a flooded area. Doing this will also give you a better idea of whether it's safe for you to cross the flooded area in your car. Once you've passed through the water, always try your brakes. This will help wipe water from their surfaces, so that they are back to normal operation when you need them.

If your car becomes stuck in deep water, don't attempt to restart the engine or you'll risk turning a big repair bill into a huge one that could write your car off. Wait for the car to dry out and get a professional inspection before trying to drive it. If you are ever unsure if it is safe to drive through flood water, or are unsure of the depth of water – find an alternative route.

What are your top tips for driving in wet weather? Let us know in the comments section below...

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