Hazard lights: when you can and cannot use them in the UK
Using hazard lights while your car is moving is only permitted in one specific situation - on a motorway or unrestricted dual carriageway to warn drivers behind you of a hazard ahead. Using them in heavy rain, in fog or as a thank-you gesture is not permitted under Highway Code Rule 116.
Do everything even faster in our app.
What the law says about hazard lights
Highway Code Rule 116 is precise. It states that hazard warning lights must not be used while driving or being towed unless the vehicle is on a motorway or unrestricted dual carriageway and the driver needs to warn following traffic of a hazard or obstruction ahead. They should only be used for long enough to ensure the warning has been seen.
While stationary, hazard lights may be used to warn that the vehicle is temporarily obstructing traffic. The rule also adds that they must never be used as an excuse for dangerous or illegal parking.
That is the full permitted use. No other situation is covered by the rule.
Is it legal to use hazard lights in heavy rain?
No. Using hazard lights while moving in heavy rain is not permitted under Rule 116. The practice is common on UK motorways and many drivers genuinely believe it makes them more visible - but it causes a specific problem that outweighs the benefit.
When hazard lights are on, your indicators do not function clearly. A driver behind cannot tell whether you are about to change lanes, slow down or turn off. In poor visibility this ambiguity is dangerous, which is precisely why the Highway Code does not permit it. In rain or fog, use dipped headlights, reduce your speed and increase your following distance. Our guide to driving in bad weather covers the full set of wet and fog weather rules.
The motorway thank-you flash
Flashing hazard lights briefly to thank a driver who has let you merge or pass is a widely used habit on UK motorways. It is not permitted under Rule 116. The rule only allows hazards while moving when warning of a hazard ahead - not as a courtesy signal in the other direction.
In practice, police rarely act on a brief two-flash thank-you. But if a moment of confusion caused by hazard lights contributed to an accident - another driver unsure whether you were signalling a lane change - the driver who activated them could face scrutiny for careless use of a vehicle control. A single headlight flash or a raised hand is the conventional alternative and has no legal risk attached.
When hazard lights are legal while moving
There is one permitted use while moving: on a motorway or unrestricted dual carriageway, to warn drivers behind you of a hazard or obstruction ahead. The typical scenario is approaching a sudden queue of stationary traffic on a fast road. Switching on hazards briefly warns drivers behind before they can see the queue themselves, buying them reaction time.
The qualifications matter: motorway or unrestricted dual carriageway only, not ordinary A-roads or urban roads. The hazard must be ahead. And you should switch them off as soon as you are satisfied the warning has been observed. Our guide to motorway driving rules explains more about hazard management and smart motorway signals.
When hazard lights are legal while stationary
Stationary use is the primary permitted situation and the one most drivers know. Hazards are appropriate when:
- Your vehicle has broken down and is blocking or partially obstructing a road
- You have had to make an emergency stop - for example, because traffic ahead stopped suddenly
- The vehicle is being towed on a rope or A-frame with the engine off
- You are temporarily obstructing traffic at a delivery point or roadside stop
The test is whether your stationary vehicle represents a genuine temporary obstruction. A car on the hard shoulder, a breakdown on a live lane or a van briefly blocking a narrow road all meet this standard.
Using hazard lights to excuse illegal parking
Leaving hazard lights on while parked in a restricted zone is one of the most common misuses. Double yellow lines, red routes, loading restrictions and bus stops are not suspended by a pair of flashing orange lights. A parking enforcement officer can and does issue penalty charge notices to vehicles displaying hazards in restricted areas.
The lights signal an intention not to stay long. They do not make the stop legal. If you are uncertain about where you can stop or park, our guide to parking rules in the UK sets out what is and is not permitted.
Stay legal on every journey
The Highway Code's hazard light rules are among the most widely misunderstood in everyday driving. Our guide to driving laws you might not know you are breaking covers more of the rules that catch experienced drivers out. And if you are borrowing a car or lending yours out, temporary car insurance gives both driver and owner comprehensive cover from one hour, with the car owner's no claims discount kept completely separate.
Frequently asked questions
Is it illegal to use hazard lights in rain in the UK?
Yes, using hazard lights while driving in rain is not permitted under Highway Code Rule 116. The rule only allows hazards while moving on a motorway or dual carriageway to warn of a hazard ahead. In rain, use dipped headlights and reduce your speed instead. Using hazards in rain prevents your indicators working clearly, which is why the rule does not allow it.
When should you put your hazard lights on?
While stationary: when your vehicle is temporarily obstructing traffic - a breakdown, emergency stop or being towed. While moving: only on a motorway or unrestricted dual carriageway to warn following drivers of a hazard or obstruction ahead. These are the only two permitted uses under Highway Code Rule 116.
Can you use hazard lights as a thank you on the motorway?
It is not permitted under Highway Code Rule 116, which only allows hazards while moving as a warning of a hazard ahead. The brief two-flash thank-you is common practice and police rarely act on it, but it is technically outside the rules. A single headlight flash or a raised hand is the permitted alternative.
Is it illegal to park with hazard lights on?
Yes, if you are parked in a restricted area. Highway Code Rule 116 explicitly states hazard lights must never be used as an excuse for dangerous or illegal parking. Double yellow lines, red routes, bus stops and loading restrictions are not suspended by hazard lights. A parking enforcement officer can still issue a fine regardless of whether your hazards are flashing.
What is Highway Code Rule 116?
Rule 116 covers hazard warning lights. It states that hazards must not be used while driving unless on a motorway or unrestricted dual carriageway to warn of a hazard ahead. While stationary, they may be used to warn that the vehicle is temporarily blocking traffic. They must never be used to excuse illegal parking.
Temporary insurance quote
Get a price in under 60 seconds!