TÜV SÜD: Safely through the storm
Driving in extreme weather conditions
TÜV SÜD: Safely through the storm
In the summer of 2011 the weather has it all, delivering periods of intense heat immediately followed by torrential rain. As a result, roads may often be under water and tunnels are flooded, creating difficult driving conditions in many areas. As soon as heavy rain hits the road surface, the entire physics of driving undergoes a sea-change as the danger of aquaplaning soars and potential accidents loom. Often drivers lose contact with the road altogether when flooding affects streets or tunnels. The TÜV SÜD experts explain why heavy rain is so dangerous and how critical situations can be mastered.
Torrential rain, thunderstorms, squalls - the German Weather Service (DWD) provides continuous announcements of bad weather and issues storm warnings that generally have little impact on drivers, yet all the more on the traffic situation. Congestion and accidents can result from flooded roads and tunnels. Drivers should be alert when extreme weather conditions threaten, especially when their route involves underpasses or even tunnels. Here extra care is required, as high water levels may cause the car's electronic systems to fail or the engine to aspirate water instead of the air required for combustion, leading to stalling. Other consequences may include malfunctioning of electrically powered convenience features like windows, or blockage of central locking systems. "A waterlogged car may rapidly become a traffic obstacle, and thus a potentially fatal trap", warns Philip Puls of TÜV SÜD. In extreme weather drivers should reconsider all journeys and switch to public transport if necessary; while this form of transport may also be halted by bad weather, it is safer than taking the car. "If your journey is essential, take time to reconsider your route and watch out for road blocks or warnings", advises Puls.
But even where flooding is not an immediate danger, driving in rain demands special attention. All drivers are familiar with a situation of bucking steering wheels, noise in the wheel arches and a general feeling of emergency – and rightly so, because aquaplaning places both drivers and the materials of their vehicles under the utmost stress. Even at speeds of 80 kilometres per hour, each tyre displaces enough water to fill a bathtub - around 150 litres - every four seconds. If a tyre fails to deliver this performance because of high speeds or insufficient tread, it 'floats' - a phenomenon known as aquaplaning. The hazards of aquaplaning are shown in studies by the German Insurance Association (GDV) in which the risk of accident doubles in rainy conditions in comparison to dry roads. "Particular care must therefore be taken when driving in rain; drivers must adjust their speed and ensure that they are fully aware of the traffic situation at all times", urges Puls.
Distance: When roads suddenly become wet, it is vital for drivers to increase their distance from other vehicles – but not by panicking and wildly steering or braking. This advice applies particularly to motorways. In sudden showers, switch on the windscreen wipers to their fastest speed, take your foot off the accelerator, gradually reduce speed, keep your eye on the traffic – and keep calm. And don't forget to move out of the fast lane after lowering your speed!
Warning: The imminence of aquaplaning can be predicted. In this situation, the road surface is usually already covered with a film of water. The loud noise of water spraying into the wheel arches or under the car body can clearly be heard. Spinning wheels or a bouncing speedometer are major warning signs. A bucking steering-wheel also shows that the wheels have temporarily lost contact with the ground. "Watch out extra carefully for these signs in rainy weather", advises Puls.
Roads: Ruts in the road significantly increase the danger for drivers – but the road surface itself also has a major role to play. Some special types of asphalt actually conduct water away from the road surface, and any incline or rise in the road supports drainage. However, the concrete road surfaces that are becoming increasingly common on motorways are particularly susceptible to aquaplaning. The professionals at TÜV SÜD advise drivers to watch out for any changes in road conditions and road surface. Be especially careful on roads with grooves or ruts, and lower your speed!
Speed: The minimum speed at which aquaplaning begins depends on a number of factors. Tyre tread naturally has a major impact. New tyres with a tread depth of seven millimetres or over are still able to deflect water at around 80 km/h. However, it is high time to replace tyres that are left with a mere three millimetres of tread – the car will start to 'waterski' from speeds of only 70 km/h. And at the legal minimum tread of 1.6 millimetres, aquaplaning is already on the cards at 50 km/h. Wide tyres have a greater tendency to 'float' than more moderate widths. Puls warns, "Change your tyres in good time – a tread between three and four millimetres is the absolute minimum."
Steering: Once the front wheels start to float steering becomes not only impossible, but practically dangerous. This is because the car initially fails to respond, but may suddenly change direction as soon as the wheels regain traction. TÜV SÜD urgently recommends reducing speed before steering, to allow the tyres to regain road grip before changing the direction of the vehicle.
Braking: Unlike steering, braking can be applied at any time – assuming the car is equipped with an ABS system at minimum, which largely prevents drifting. Do not be too cautious when applying the brakes! ABS will rule out overbraking. As an additional tip, TÜV SÜD recommends lightly braking every now and then when driving in wet weather. This dries out the brake linings and disks and enables them to act faster in an emergency. Incidentally, today's premium vehicles do this automatically without the driver even noticing.
Editor: Frank Volk