Clearing snow and ice from your car: what the Highway Code says

On a frosty morning it is tempting to scrape a letterbox-sized hole in the windscreen and set off. It is also one of the easiest ways to end up driving half-blind, and the Highway Code is clear that a peephole is not enough. This guide explains what the rules actually say about snow and ice, why leaving the engine running on the street is a problem, and a simple routine that gets you on the road safely without risking damage to the glass.

What the Highway Code says about snow and ice

The key rule is Highway Code Rule 229, which covers driving in icy and snowy weather. Before you set off, you MUST be able to see, so you should clear all snow and ice from all your windows – not just the windscreen, but the side windows and rear screen too. The same rule says you MUST ensure your lights are clean and your number plates are clearly visible and legible.

Rule 229 goes further. It says you should make sure your mirrors are clear and your windows are demisted, and that you should remove all snow that might fall off into the path of other road users. That last point is the one people most often skip. A thick layer on the roof can slide forward over the windscreen the first time you brake, or lift off in a sheet onto the car behind once you pick up speed.

The Code's Annex 6 on vehicle maintenance, safety and security adds that windscreens and windows MUST be kept clean and free from obstructions. A screen that is still partly iced over or fogged up on the inside is hardly free from obstruction, so the sensible approach is to treat Rule 229 and Annex 6 together as a checklist and work through the whole car, not only the parts written in capitals.

Is it illegal to drive with snow on the roof?

The Highway Code does not single out the roof by name, but Rule 229 tells you to remove all snow that might fall off into the path of other road users – and a roof, bonnet or boot lid piled with snow is exactly where that comes from. So clear the whole car: roof, bonnet, boot, lights, number plates and mirrors, as well as every window.

We are not going to quote penalties here, because what happens in any individual case depends on the circumstances. The practical test is simple: could anything on your car block your view, hide your lights or plates, or land on somebody else? If the answer is yes, keep clearing.

Can I leave the engine running to defrost the car?

Rule 123 of the Highway Code says you MUST NOT leave a parked vehicle unattended with the engine running, and you MUST NOT leave a vehicle engine running unnecessarily while stationary on a public road. So starting the car and popping back indoors for a cup of tea while it warms up on the street is out.

An unattended car with the engine running is also an easy target for opportunist thieves, and it is worth checking what your insurance policy says about that situation. The practical answer is to do the clearing by hand with a scraper, a snow brush and de-icer, then start the engine and use the heater and blower to keep the glass clear as you set off.

How to defrost a windscreen quickly and safely

A good routine takes a few minutes. Work through it in this order:

• Snow first, from the top down. Use a soft snow brush to clear the roof, then the bonnet and boot, then the glass. Working downwards stops you dropping snow onto windows you have already cleared.
• Apply de-icer. Spray it across the frozen glass and give it a moment to soften the ice before you start scraping.
• Scrape with a plastic scraper. Keep the blade fairly flat to the glass and use firm, steady strokes. Avoid anything metal or sharp that could scratch the screen,.
• Do every window and both mirrors.
• Free the wipers before you switch them on. A blade frozen to the glass can tear, and a wiper motor straining against ice will not do it any favours. Lift gently or let the de-icer work around the rubber first.
• Clean the lights and number plates. Brush off snow and wipe away road grime and frost so they are visible and legible, as Rule 229 requires.
• Demist the inside. Once the engine is running, direct the blower to the windscreen, switch on the heated rear screen and, if your car has air conditioning, use it – it helps dry the air. Switch off recirculation so damp air is not being pushed round the cabin.

Why not use boiling water?

A kettle of hot water looks like a shortcut, but pouring very hot water onto frozen glass exposes it to a sudden temperature change, and that risks cracking the windscreen – particularly if there is already a small chip. The water can also refreeze on the glass and wipers. De-icer and a scraper are slower but far kinder to the glass.

Stop the frost forming in the first place

The quickest windscreen to clear is one that never frosted up. A few habits help:

• Use a windscreen cover overnight. A cover laid over the outside of the screen and held in place by the doors or straps takes the frost instead of the glass. In the morning you lift it off, shake it out and store it in the boot. Our windscreen sunshades and frost screens collection includes screen covers; some are designed to double up as a sun shade in summer, so check the description for how each one fits.
• Keep the cabin dry. Wet floor mats, damp coats and umbrellas left in the car all add moisture that ends up as condensation or even ice on the inside of the glass.

Cold-weather checks under the bonnet

Clear glass is only part of winter readiness. With the engine cold, check the coolant level against the marks on the expansion tank and top up with the type of antifreeze your vehicle handbook specifies. Check the washer reservoir is full of a screenwash suitable for low temperatures, so the jets and pipes do not freeze just when a gritted road starts coating the screen with salt spray. It is also a good moment to check the engine oil level.

Rule 228: the winter kit the Highway Code suggests

Rule 228, on the same Highway Code page on adverse weather, suggests carrying an emergency kit in winter: de-icer, an ice scraper, a torch, warm clothing and boots, a first aid kit, jump leads and a shovel. If you want a fuller list with notes on each item, see our winter car kit checklist for UK drivers.

What to keep in the car this winter

You do not need a boot full of gadgets, just the right basics in a place you can reach them. Our winter and emergency collection brings together cold-weather and roadside emergency essentials in one place. For the engine bay, the antifreeze and coolant range covers coolant for topping up – always match the type to your handbook – and the wider oils and fluids collection covers engine oils and other fluids worth checking before the cold sets in. Keep the kit together in the boot and a frozen morning becomes a five-minute job.

Frequently asked questions

Is it illegal to drive with snow on your car roof in the UK?

Highway Code Rule 229 says you should remove all snow that might fall off into the path of other road users, and that you must be able to see. The safest approach is to clear the roof, bonnet and boot as well as every window before you drive.

Can I leave my car running on the street to defrost it?

Highway Code Rule 123 says you must not leave a parked vehicle unattended with the engine running, or leave an engine running unnecessarily while stationary on a public road. Clear the ice by hand with a scraper and de-icer, then use the heater once you set off.

Is it OK to pour hot water on a frozen windscreen?

It is not a good idea. The sudden temperature change risks cracking the glass, especially if there is already a chip, and the water can refreeze on the screen and wipers.

Do I have to clear my number plates and lights?

Yes. Rule 229 says you must ensure your lights are clean and your number plates are clearly visible and legible, so brush off snow and wipe away frost and grime.

Do windscreen frost covers actually help?

A cover fitted over the outside of the windscreen overnight takes the frost instead of the glass, which can save a lot of scraping. Make sure it is secured properly and removed completely before you drive.