Driving through flooded roads
Roads seldom flood for any great distance, as the water runs down to fill the low spots. In dips, the water can be quite deep, so it is a good idea to test the depth with a stick first to make sure that you'll be able to get through. Standing water, even when it is shallow can cause aquaplaning. Water under trees and in other areas of shade will be the last to dry.
The assumption that the good grip of modern tyres means you are always safe on wet roads in a dangerous fallacy. Driving in the rain is always hazardous, but the dangers are not just related to skidding. Lack of visibility can create dangerous situations leading to sudden accidents.
Visibility
Loss of visibility in heavy rain can be worse than in fog, to such an extent that drivers sometimes can't see at all in a really torrential downpour. Even if the wipers and demisters can keep the windscreen clear, it is often impossible to see through the thick blanket of rain around you.
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If conditions are as bad as this, then it is too dangerous to carry on. If there is so much traffic that you can't leave a large enough gap between you and the vehicle in front, or if you're pressurized by the vehicle behind into travelling more quickly than you'd like, the answer is to get off the road and stop.
Spray from heavy vehicles is a particular problem on motorways and trunk roads, where the large road surface area collects a lot of water and drains slowly because of its lack of camber. It's best to hang back out of the spray until the vehicle causing it moves over to the inner lane, or until the gradient gives better drainage.
In heavy rain, steer well clear of vehicles with their rear fog lamps on. The rain diffuses the strong red light, making it very difficult to see the car's brake lights when they come on, as well as possibly having a dangerous mesmerizing effect. Despite advertizing campaigns, many drivers still use these lights wrongly; they should only be used where visibility is impaired by fog, snow or sleet.
Wet weather grip
A wheel simply rolling along the road in a straight line is in no risk of skidding or sliding, whatever the condition of the surface. Only when you try to change its speed or direction can grip be lost. How easily this can happen depends on the amount of grip available in the first place.
Many country roads offer more grip in wet weather than heavily trafficked ones in town, even though rural roads may harbour more standing water. Mud and wet leaves are very slippery, but at least you can often see them and slow down before you reach them, and take care with braking and steering while you are on them.
On roads that have begun to dry out, remember that the road will remain slippery for longer under trees and other areas of shade.
Driving through deep water
If you have to drive through a flood, keep the engine revs up to stop water entering the exhaust pipe. Too much speed will create a bow wave which could flood the engine, but you'll need a stab of extra throttle if you are leaving a ford by a bank.
Apply the brakes to dry them when you get out of the water - this can take some time with drums.
The most treacherous surfaces, though, are those that have just received light rain after a dry period. The water, mixing with road and rubber dust, leaves a very slippery emulsion on the road surface particularly tricky in towns or on any other smooth tarmac where the surface is not generally very grippy to begin with.
On any surface you're not sure of, therefore, make your steering smooth and gentle, and brake lightly at first, pushing progressively harder on the pedal until you're sure how much grip is available.
In any case, when the roads are wet it is always wise to begin braking earlier than if you were on dry roads. If a skid does develop, you'll have time and distance in hand to release the brakes and apply them again more gently than before.
Standing water
Fords and marker posts
These rarely have a consistent water level and unless you are familiar with the crossing it is wise to get out of the car to see how deep the water is first.
Some fords have marker posts set into the ground so you can check the water level at a glance. As a rule, any water which will come above the level of the door bottom is probably too deep for the car, although the engine will usually keep running in water up to 60cm deep.
The problem with standing water is that you can't see how deep it is. Most cars cope with puddles and standing water quite well, but be ready for possible aquaplaning where a wheel rides up on a ramp of water and loses all grip.
Some front-wheel-drive cars are prone to sudden aquaplaning when accelerating over standing water. This usually happens when you are accelerating past another vehicle on a narrow road and the offside wheels go through puddles in the right hand gutter. When the powered wheel lifts off the tarmac and spins, you lose both steering control and acceleration. Be ready, therefore, to reduce power quickly to restore traction and control. If the wheels lock again, repeat the exercise - this is called cadence braking.
A far better approach is to look further ahead and avoid overtaking if you will have to accelerate through standing water.
