When Should You Use Your Hazard Warning Lights?

close up of car stereo and hazard warning button

Learning to drive isn’t just about practising your steering, following road signs and keeping a safe distance from other road users; you also need to be able to use the different bells and whistles (well, horns and switches) inside your car correctly. One of the buttons on your dashboard that you may not have to use very often—if at all—in your lessons, but is essential to know about for your theory test and for your post-test driving career, displays a triangular warning symbol: the one that activates your hazard warning lights.

Not entirely clear on the rules? Not to worry: we’ll cover what your hazards do, when you’re allowed to turn them on, and how you should keep them going long for.

What are hazard warning lights for?

Your hazard warning lights are, quite simply, a way to warn other road users that there is danger ahead. When activated, all four of your indicators will blink at the same time, and will continue to do so until you manually turn them off. Any other lights that normally illuminate when your indicators are on—some cars have indicating lights on their wing mirrors, for example—will also flash orange.

How can I activate my hazards?

Make sure you know where your hazard light button is located in your vehicle before you begin to drive it; in an emergency, you won’t have time to search around for it. The button’s usually fairly obvious, particularly as it’ll be quite big and there will be some red on it: either white triangles on a red background, or red triangles on a black background.

The triangle will illuminate when you’ve pressed it, and both your left and right dashboard indicator lights will also flash intermittently, to remind you that they’re on.

When can you use your hazard lights?

Using hazard lights when you’re stationary

Woman looking under the bonnet of her broken down car

Just as it does with other lighting requirements, the Highway Code covers when you should use your hazard warning lights. According to Rule 116, you can use your hazards to convey danger when you’re stopped in order to indicate to other road users that you are ‘obstructing traffic’. This could be because you’ve had an accident or are waiting for an obstacle in the road to move before you proceed.

You should always make sure you turn on your hazard warning lights if you’ve broken down, too—even if you’re technically out of the way of other traffic, such as on the hard shoulder or in a lay-by.

These rules apply regardless of the level of daylight: your hazard lights will help to bring attention to a potentially dangerous situation even if the sun is shining.

Can you drive with your hazards on?

The rules on when you should use hazard warning lights are more limited when you’re driving or being towed. In fact, you should never use your hazards when moving unless you need to warn those behind you of danger ahead and you are on a motorway, or an unrestricted dual carriageway.

What is an unrestricted dual carriageway?

Where there are no enforced speed restrictions on a road, the speed limit reverts to the national speed limit. In the UK, you can drive at 70 mph on an unrestricted dual carriageway.

If both these conditions apply, you may stick your hazards on—but then only for as long as it takes to make sure your warning has been seen: usually just a few seconds.

One common example of legitimately using your hazard lights when driving is if you suddenly come upon a queue on the motorway. Your hazards will let others know that you’re braking sharply, and help them to apply their brakes in good time, to prevent them from crashing into you and causing a pile up.

On the other hand, you should never use your hazard lights when you’re driving slowly looking for a turning. Your indicators will not work until you’ve disabled your hazard lights, so nobody will be able to tell if and where you intend to turn. If you then turn right, as another vehicle attempts dangerous overtake, the consequences could be catastrophic.

Hazard lights when parking illegally

A traffic warden giving a parking ticket

You’ve probably witnessed vehicles parked on double yellow lines employing their hazards—almost as an excuse for doing do. “I won’t be long”, they seem to say. However, the Highway Code warns against this sort of behaviour: using them to apprise others of your own dangerous or illegal parking is no excuse and will not prevent you from getting a parking ticket.

It’s particularly dangerous to use your hazards when stationary in front of other parked vehicle. Traffic coming up behind you will likely only see one indicator, which will tell them that you’re planning to pull out; in this case, they make your illegal parking even more hazardous!


① Do hazard lights come on automatically in an accident?

Some modern cars now offer hazards that will activate automatically when they detect a collision—just as airbags do. They may also come on if you brake very suddenly, like in an emergency stop situation.

However, many cars do not have this feature—so if you’re caught in an accident, and are able to, make sure you press that red triangle to alert others to the danger.

② Will any faults with my hazard warning lights impact upon my MOT?

If you notice either of your indicators failing, you need to sort it out as soon as possible: it’ll diminish the effectiveness of your hazards. An MOT will also flag up if any of your lights don’t work—but fortunately, it’ll usually just be a case of getting your bulb replaced.

③ Will my hazard lights drain the battery?

Hazard warning lights are essential for road safety, so they are designed to use minimal battery. Of course, if they are kept on indefinitely, they will eventually wear the battery down—but for the most part they’ll work for as long as you need them to,

Clear on when and how to use your hazards? There’s plenty more advice where that came from! Check out our blog for all the latest hints, tips and guides.

By Katie Scott

Katie grew up in the middle of nowhere, so knows the true value of getting behind the wheel. From the rules of the road to handy hints and tips, she'll give you the lowdown on all things driving. Always on the move, when she's not in the car, you'll probably find Katie darting around the squash courts or out running in the rainy British countryside.


  1. Reply



    I am wondering if hazard lights must not be used with any other light in car. Like parking light or fog lights?

    1. Reply

      Andy Boardman

      Hi Alireza,

      In general, you shouldn’t be using your hazard lights while driving. The only exception is to warn other drivers of an upcoming hazard when you’re driving on a motorway or unrestricted dual carriageway, which you should do for as brief a period as practicable. There may be some instances, therefore, where you use hazard lights alongside other lights—but these are very limited.

      Hope this helps.


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