You may use hazard warning lights when your vehicle is stationary and temporarily obstructing traffic, and while moving on a motorway or unrestricted dual carriageway to warn drivers behind you of a hazard or obstruction ahead. That is it. The Highway Code (Rule 116) does not allow them for a quick stop on double yellows, a wave of thanks, or driving through heavy rain.
That one-line answer is what the theory test is checking, and it is the bit most learners get slightly wrong. So let me unpack it properly, from the passenger seat, because there is a fair amount of folklore attached to that little red triangle button.
When may you use hazard warning lights?
The rule that governs this is Rule 116 of the Highway Code. It is short, and it splits into two halves: a stationary use that is always fine, and a single moving exception. Here is the full picture in one place.
| Situation | Allowed? | Highway Code basis |
|---|---|---|
| Stationary and temporarily obstructing traffic (broken down, stopped in a live lane) | Yes | Rule 116 |
| Broken down and causing an obstruction | Yes | Rules 116 and 276 |
| Moving on a motorway or unrestricted dual carriageway, to warn traffic behind of a hazard or queue ahead | Yes (briefly) | Rule 116 |
| Being towed, only to warn other drivers of a hazard | In practice, only as a warning | Rule 116 |
| Stopped in normal queuing traffic or at lights | No | Rule 116 |
| Parked illegally (double yellows, zig-zags, pavement) | No | Rule 116 |
| Driving normally in rain, fog or snow | No, use lights instead | Rule 116 / Rule 226 |
| As a “thank you” or to invite someone through | No | Rules 110 and 111 |
Read Rule 116 slowly and you will notice it is written as a near-total ban with two carve-outs. The default position is that hazard lights stay off. They come on only to say one thing to other road users: “I am a hazard, or there is a hazard right here.” Nothing else.
The stationary use: broken down or blocking the road
This is the one everybody agrees on. If your car has stopped where other drivers would not expect it, and it is causing an obstruction, your hazard lights go on. A stall at a busy junction, a breakdown on a fast road, stopping on a blind bend because the car in front has stopped – all fair game.
Rule 276, which covers breakdowns, backs this up: warn other traffic by using your hazard warning lights if your vehicle is causing an obstruction. If you carry a warning triangle, the Highway Code says place it on the road at least 45 metres (147 feet) behind the vehicle, on the same side, and take it up again before you drive off. One firm exception: never use a warning triangle on a motorway, because walking out to place it puts you in real danger from traffic.
Here is the bit that catches people out on a fast road. If you break down on a motorway, Rule 277 is clear about the order of play: get into the left lane, pull into an emergency area or onto the hard shoulder if you can, switch your hazard warning lights on, and leave the car by the door furthest from the traffic. Then get behind the barrier if there is one. The hazard lights matter, but they are step three, not step one.
The moving exception: motorways and unrestricted dual carriageways
This is the only time the Highway Code lets you flash your hazards while the car is actually moving. Rule 116 permits it on a motorway or unrestricted dual carriageway when you need to warn the drivers behind you of a hazard or obstruction ahead – typically a wall of brake lights appearing as traffic slows suddenly to a crawl.
A few things learners misread here:
- It is a brief warning, not a state you drive in for miles. Flick them on, let the traffic behind register the message, then switch them off. Five seconds or so is usually enough.
- “Unrestricted” means a dual carriageway subject to the national speed limit (the white circle with a black diagonal). If it is a 40 or 50mph dual carriageway, this exception does not apply.
- If you want to know exactly what counts as one of these roads, it is worth reading up on what a dual carriageway actually is, because “dual carriageway” and “motorway” are not the same thing and the speed rules differ.
- It is a warning to the traffic behind you. You are passing on a message about danger ahead that they cannot see yet.
On any ordinary single-carriageway road, moving, this does not apply. You slow down, brake in good time, and let your brake lights do the talking.
When you must not use hazard warning lights
Most of the marks lost on this topic come from the “must not” list, not the “may” list. Here is where drivers, learners included, get it wrong.
Do not use them to excuse dodgy parking. Sticking your hazards on while you nip into the shop does not make it legal to sit on double yellow lines, on the zig-zags by a pedestrian crossing, or half on the pavement. The lights change nothing about the parking restriction. This is probably the single most common real-world misuse.
Do not use them in normal traffic queues or at lights. People do it, thinking it is polite or clearer. It is not. Rule 116 does not cover it, and in a slow queue it just muddies the message for the driver behind, who cannot tell whether you have a genuine problem.
Do not use them instead of indicators. If you are turning, pulling over or changing lanes, that is what your indicators are for. Hazards tell nobody which way you are going.
Do not use them in bad weather while driving. Heavy rain, fog or falling snow are jobs for dipped headlights and, in fog, fog lights (Rule 226 covers using lights in poor visibility). Driving along with hazards on hides your indicators and confuses everyone.
Do not use them as a “thank you”. This one feels harmless, and half the country does it. But strictly it is not a Highway Code signal at all. The code is deliberately tight on informal signals: Rule 110 says only flash your headlights to let others know you are there, not to convey any other message, and Rule 111 says never assume a flash is an invitation to proceed. The same logic applies to a friendly double-tap of the hazards. On test, keep signals to what the code recognises.
Why this matters on your driving test
Hazard lights show up in two places: the theory test, where you will get a multiple-choice question almost word for word from Rule 116, and, occasionally, the practical, if you ever need them for real.
On the practical test, an examiner is not going to ask you to demonstrate hazard lights. What can cost you is using them wrongly – most often as a substitute for proper observation, signalling or planning. If you flick the hazards on because you are dithering at a junction, or to “apologise” for a clumsy manoeuvre, that is the sort of thing that reads as a lack of control. The examiners are watching for calm, correct signals. If signalling is a weak spot for you, our guide to passing the driving test first time walks through the habits that keep you on the right side of a marking sheet.
For the theory test, memorise the two allowed situations and the fact that everything else is out. The classic trick question offers you four tempting options – warning oncoming traffic that you intend to stop, thanking a driver who let you out, double-parking briefly, and warning traffic behind on a motorway of a hazard ahead – and only the last one is correct. If you can explain why the other three are wrong, you will never lose that mark. That kind of understanding-over-memorising approach is exactly what a good intensive course drills into you, the same way it does with the rules for approaching roundabouts.
A quick word on where GetMyPass fits
Learning the Highway Code cold is one thing; using it instinctively at 60mph on a dual carriageway is another. On a GetMyPass intensive driving course, you cover rules like this in context, actually on the roads where they apply, so the knowledge sticks. If you have had a handful of lessons already and want to consolidate fast, our Advanced intensive course is built for exactly that stage. Prefer to see the shape of it first? Here is how our courses work, start to finish. We get you genuinely test-ready – confident, safe, and clear on the rules examiners actually mark.
Frequently Asked Questions
When may you use hazard warning lights?
You may use them when your vehicle is stationary and temporarily obstructing traffic (for example, broken down or stopped in a live lane), and while moving on a motorway or unrestricted dual carriageway to warn drivers behind you of a hazard or obstruction ahead. Highway Code Rule 116 does not allow them in any other situation.
When may you use hazard warning lights while you are driving? (theory test)
The theory-test answer is: only on a motorway or unrestricted dual carriageway, to warn traffic behind you when you slow down suddenly because of a hazard or obstruction ahead. You must not use them while moving on ordinary roads, and never to excuse dangerous or illegal parking. This comes straight from Rule 116.
When may you use your hazard lights on a motorway?
Use them if you break down and are causing an obstruction (with the car in the left lane, an emergency area or the hard shoulder), and briefly while moving to warn the drivers behind you of a sudden queue or hazard ahead. Turn them off once the warning has been noticed – a few seconds is usually enough.
Can you use hazard warning lights when parked or stopped in traffic?
No. Rule 116 does not cover using them in a normal traffic queue, at traffic lights, or to make illegal parking acceptable. They are only for warning others that you, or something right in front of you, is a genuine hazard. Putting them on while double-parked or on double yellow lines does not make it legal.
Is it illegal to use hazard lights as a “thank you”?
It is not a recognised Highway Code signal, and the code is deliberately strict about informal ones. Rule 110 says only flash your headlights to let others know you are there, and Rule 111 says never treat a flash as an invitation to proceed. The safest approach, and the correct one for your test, is to stick to the signals the code recognises rather than improvising a thank-you.
How long should you leave hazard warning lights on while moving?
Only for as long as it takes the traffic behind you to register the warning – typically around five seconds. They are a brief alert on a motorway or unrestricted dual carriageway, not something you drive along with. Once drivers behind have slowed and seen the hazard, switch them off so your normal indicators work again.