Drivers warned over little-known air-con rule which everyone must follow

Following this often-overlooked driving rule can make a significant difference for Brits - and could even help to reduce the risk of accidents during the scorching summer months
Motorists have been issued a fresh reminder about the rules related to using air conditioning in their motors during the summer months.
As temperatures rise and heatwaves increase in intensity and frequency across the UK, drivers should heed an important yet often overlooked rule in the Highway Code related to vehicle ventilation. With temperatures expected to reach well over 30C in June 2025, motorists must be extra vigilant in regards to how they keep their cars cool and safe.
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Many people instinctively turn on the air conditioning or wind down their windows to stay comfortable during hot weather, but did you know that the Highway Code explicitly advises drivers to keep their vehicles well ventilated to prevent drowsiness? This rule is particularly relevant during heatwaves, when the interior of a car can become dangerously hot and stuffy — increasing the risk of fatigue behind the wheel, which can lead to accidents.
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The Highway Code specifically states: "Keep your vehicle well ventilated to avoid drowsiness. Be aware that the road surface may become soft or if it rains after a dry spell it may become slippery. These conditions could affect your steering and braking."
This advice is crucial because a lack of fresh air inside the vehicle can make drivers sleepy and therefore less alert, significantly increasing the chances of an accident. A spokesperson for online driving instructor marketplace EzLicence, Joe Parry, emphasised the importance of taking precautions.
He said: "The warmer weather is bound to heat our cars' interior. However, few realise that Rule 237 of the Highway Code states that vehicles must be ventilated in the heat to avoid drowsiness. So, keeping the window open when possible or using the air conditioning is essential, especially if you're sitting in traffic."
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But ventilation isn't the only aspect of driving during a heatwave the Highway Code addresses: "If you are dazzled by bright sunlight, slow down and if necessary, stop." Bright sun glare can seriously impair vision, at least temporarily, further reducing your ability to react quickly, which makes it vitally important to take precautions such as wearing sunglasses and sun visors, or even pulling over when visibility is severely impaired.
With the extremely hot weather conditions, Brits are also being advised to remove a number of everyday items from their cars. On a day when the temperature outside is 30°C, the interior of a vehicle can reach around 50°C within half an hour.
The rapid temperature rise is caused by the greenhouse effect — where sunlight passes through the glass windows and heats the interior surfaces, but the heat cannot escape easily, causing the inside temperature to soar well above the outside temperature. For example, lighters left in direct sunlight can explode, sometimes resulting in fires that damage the car's interior, crack windshields, melt dashboard components or worse — cause injury. Find the full list of items to remove from your car here.
With heatwave conditions highly likely to persist, and even increase in the coming years due to climate change, drivers should take this advice seriously. Ensuring good ventilation inside the car not only improves comfort — it enhances safety by helping to keep drivers alert and focused on the road. Whether by cracking a window or turning on the air conditioning, following this little-known rule can make a significant difference in preventing heat-related fatigue and reducing the risk of crashes during the scorching summer months.

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