Winter brings foggy conditions especially from late afternoon to early morning when the temperature drops. Fog reduces visibility and increases the risk of a crash. This highlights the importance of driving to the conditions and using lights so your vehicle is more easily seen.
When driving in fog it is important to slow down. Slowing down will reduce the stopping distance and the time taken to stop. In fog the distance that can be seen ahead is drastically reduced and it may be necessary to react and stop quickly.
In very thick fog make sure you always know where you are on the road and never drive at a speed that forces you to guess what is ahead. Line marking, reflectors and guide posts can provide guidance. Overtaking should be avoided.
When driving in any weather conditions with reduced visibility, your vehicle must have clearly visible headlights, tail lights, number plate lights and, if fitted to your vehicle, clearance lights and side marker lights. Now is a good time to clean your lights and check they are all working, this should be done regularly.
To improve visibility when in fog, drivers should use headlights on low-beam. The powerful light emitted from high beam will be reflected in the fog’s water molecules causing glare making the headlights less effective than on low beam.
Some cars have fog lights that are designed to reflect a horizontal band of light across the front of the vehicle, and a special shield built inside the light prevents the beam from being projected upwards.
Front and rear fog lights must only be used in fog or rain, or when conditions such as smoke and dust limit your vision. It is a legal requirement that once conditions improve and you can see more clearly, the front and rear fog lights are switched off.
Foggy windows are also a problem during the colder months. Foggy glass reduces visibility and it is important to have a clear windscreen and windows when driving. It is an offence to drive a vehicle without a clear view.
Air inside a vehicle is usually warmer and more humid than the air outside. Car windows and windscreens will become foggy on the inside when the warm air inside comes in contact with the glass, which is cool from the outside temperature.
To clear foggy windows, leave the air conditioning switched on with the heater set at a comfortable warm temperature and the re-circulation feature turned off to allow fresh air to enter. Alternatively, cars may have a demister function which turns on the air-conditioner and fan to force dry warm air onto the windscreen. Most cars have a rear window defroster which uses an electric element to warm the glass which should also be used.
The oil, dust and other contaminants that build up on your windows gives water vapour more surface area on which to hold. Clean glass reduces the amount of area these tiny droplets love, meaning your car’s glass will take longer to steam up in the first instance, and be quicker to clear with the methods above once foggy.
Foggy conditions are unavoidable during winter months. Regular cleaning of your windows and lights prepares your vehicle. However, driving in these conditions may be avoided by delaying your trip or planning to travel when fog is unlikely. If you must drive in fog slow down, maximise both how far you can see and your vehicle’s visibility to others. Remember to always drive to the conditions.
