The RAC has issued a stark warning to every driver in the UK: driving off with a misted-up windscreen is against the law. Motoring experts from RAC Drive stress that obscured vision is not just hazardous but a direct breach of road traffic regulations, which can lead to prosecution.
Why Your Windscreen Mists Up
According to the RAC, the fogging on your car's interior glass is caused by water vapour. This occurs when the warmth from your body and your breath heats the air inside the vehicle, increasing its capacity to hold moisture. When this warm, moist air hits the cold surface of the windscreen, it condenses, creating that familiar and dangerous foggy layer.
The Fast and Effective Demisting Method
To clear your view quickly and safely, the RAC recommends a specific technique. Start your car's heater on a cold setting, then gradually increase the temperature as the air inside begins to dry. This prevents the cabin from being flooded with hot, 'wet' air that can make the problem worse.
Direct the airflow towards the windscreen and side windows. Even cold air from the blowers will be warmer than the icy glass, helping to dry it through evaporation and warming the glass to stop further condensation. If you are feeling cold, you can point some warm air towards yourself, but be prepared for the demisting process to take a little longer.
The RAC's clear instruction is: "just don’t move off until all glass surfaces on your car are clear. It’s dangerous and illegal if visibility is impeded".
Using Air Conditioning and Troubleshooting Issues
If your vehicle is equipped with air conditioning, use it in tandem with the heater. The experts explain that while hot air dries the glass, it can cool and condense again. The air-con system works to keep the cabin atmosphere dry, speeding up the clearing process.
Should your car fail to demist effectively, the issue often lies with the air conditioning or climate controls. The first step is to set the heater to its maximum temperature, direct all airflow to the windscreen, ensure the air-con is on, and turn the air recirculation function off.
If problems persist, the RAC advises seeking professional help. A trusted local garage can check for airflow and filter blockages, a malfunctioning heater or thermostat, or simply a need to top up the coolant system.
