Can you drive with a cracked windscreen?

So one day you notice a crack on your windscreen, and you’re not quite sure where you got it. Maybe you drove through some road works or were driving behind a lorry for a bit. Depending on where the crack is, and how much of the windscreen it damages, you may not be able to legally drive that car anymore.

If the crack is in your line of sight when you’re sitting in the driver's seat, you could only drive legally if the damage is less than 1cm round — about a pencil end or less. This is considered Zone A, legally defined as the 290mm centred on your steering wheel and within the sweeping range of your windscreen.

Zone B is everything else, and can have 4cm (40mm) of damage.

As well as affecting your ability to pass your MOT, a cracked windscreen could get you a fine if you’re caught on the road with it. If you have a cracked windscreen and then have an accident, it could be made even more serious if the fault of the accident may be with you because of the cracked windscreen.

How much to repair a cracked windscreen?

Costs of repairing a windscreen depend on the damage. For a chip, the average cost at the time of writing ranges from £40-£120. To replace a windscreen it ranges anywhere from £200-£800, with the average cost for a mid-range car windscreen replacement being £337.

Is a cracked windscreen an MOT failure?

Oftentimes, yes, a cracked windscreen is an MOT failure. Damage of more than 10mm in Zone A or 40mm in Zone B will probably be audited as a major or dangerous fault for your car because of how it affects your visibility while driving.  

As well as probably failing your MOT, if caught on the road with this damage, the officer could find you up to £2,500 and give you 3 penalty points.

How fast does a windshield crack spread?

How fast a windscreen crack or chip spreads depends on a few things, one of them being the weather. Sudden temperature changes (heat in cold weather, cold in hot weather, day to night etc) in particular can accelerate the growth of a crack. So if you’re someone who is getting around quite a bit in frosty weather, it may be worth looking into a heated windscreen.

Generally, though, cracked windscreens can crack further a lot faster than you may think. Within a matter of days a crack could go from being smaller and manageable with a repair kit to needing a full windscreen repair.

Importantly, a cracked windscreen makes accidents more dangerous because it reduces the structural integrity of your car — if you have an already cracked screen and wind up rolling in an accident, the roof is more likely to cave in if you have a cracked windscreen.

A cracked windscreen in an accident also means airbags are less likely to be successfully deployed, as they actually rely on the windscreen as a barrier to help reduce impact and damage to the passengers, so when it’s not structurally sound an airbag deploying may actually shatter your windscreen and injure you.

How do I stop my windscreen crack from spreading?

Honestly, one of the most straightforward ways to stop a crack from spreading is to arrange for it to be fixed or filled as soon as you notice it, just the same as if you start seeing cracks in your home’s foundations. Chips will likely be filled with resin, epoxy or acrylic and similarly repaired if a crack is smaller than 10mm, or 1cm.

Oftentimes anything larger than 10mm damage in Zone A or 40mm elsewhere means a full replacement of the windscreen.

While you’re waiting for your repair or replacement, the general advice is not to drive your car in the meantime. Road debris, potholes or otherwise uneven driving surfaces, weather… all of these conditions can make the crack in your windscreen worse, and potentially dangerous to you.

Imagine driving over a pothole and your weakened windscreen shatters entirely. Not a fun thought. Unless you have no other option, then, it’s worth doing your best to not drive the car while waiting for repair.

How do I avoid cracking my windscreen?

While sometimes you can’t avoid cracking your windscreen, a few good rules to help reduce the opportunities include:

• Regularly replace your wiper blades: this will help prevent build up from dirt and debris
• Regularly check your windscreen for small cracks and chips: the earlier you find them, the less likely they are to get larger and become a bigger issue to manage.
• Practice safe driving and keep distance: when you keep distance between yourself and other vehicles on the road, it’s less likely gravel and stone or other debris will fall on your windscreen
• Use an ice scraper or de-icing spray: on frosty mornings, as tempting as it may be to use hot water on your windscreen to quickly get going, the temperature shock can cause cracks in your windscreen
• Try to find shade on hot days: for the same reasons, finding shade on hot days can help prevent temperature shock to your glass on hot days, particularly if you use your aircon frequently

A few final thoughts…

If you notice a crack or chip in your windscreen, try and get it fixed sooner rather than later. Damage and cost to repair can escalate quickly, and can become quite dangerous for your and your passengers.