Quick answer
Place a warning triangle on the same side of the road at least 45 metres (147 feet) behind your broken-down vehicle, walking back facing the traffic. Put it further back before bends or hill crests, and switch on your hazard lights too. Never use one on a motorway.
A warning triangle is a folding red reflective triangle you set up behind a broken-down or stopped vehicle. Its whole job is to give approaching drivers extra seconds of warning so they can slow down or move over before they reach you. On a dark evening or a fast rural road, those seconds can be the difference between a near-miss and a collision.
The key numbers to remember are simple: on an ordinary road, place the triangle on the same side of the road as your vehicle, at least 45 metres (147 feet) behind it. Walk back facing the oncoming traffic so you can see any danger, and put the triangle even further back if you're near a bend or the brow of a hill where drivers can't see you until the last moment.
There is one big exception that trips people up, and the theory test loves to check it: you must never use a warning triangle on a motorway. Setting one up would mean walking a long way down the hard shoulder in fast-moving traffic, which is far too dangerous. This guide walks you through the rules, the mistakes learners make, and how to stay safe.
Study time
28 min
Level
Advanced
Confidence
+10%
Practice
15 Qs
What you'll be able to do
- Understand exactly what to do, and in what order, if you're first to arrive at a crash.
- Understand the simple, safe things you can do for an injured person until help arrives.
- Understand what to do if you break down — and the one place you must never use a warning triangle.
The facts that matter
- A warning triangle is a red reflective triangle that warns other drivers of a broken-down or stopped vehicle ahead.
- On an ordinary road, place it on the same side, at least 45 metres (147 feet) behind your vehicle.
- Walk back to position it while facing the oncoming traffic, so you can see approaching danger.
- Place it further back before a bend or the brow of a hill so drivers get more warning.
- Never use a warning triangle on a motorway — walking the hard shoulder in fast traffic is too dangerous.
- Always switch on your hazard warning lights as well, and retrieve the triangle carefully once it's safe.
Make it stick
Memory anchors
45 and facing
Two things to lock in: 45 metres back, and face the traffic as you walk. "45 and facing" keeps both the distance and your safety in one short phrase you can recall under pressure.
Motorway means no triangle
On a motorway there's no safe walk to place one, so the answer is always no. If a question mentions a motorway and a warning triangle, the correct move is: don't use it — use hazard lights and get behind the barrier.
Stay sharp
The mistakes everyone makes
Placing it too close
Setting the triangle just a few metres behind the car gives drivers almost no time to react. The rule is at least 45 metres on an ordinary road, and more before bends or hills. Too close is barely better than nothing.
Using one on the motorway
Many learners assume a triangle is always the right thing to deploy. On a motorway it isn't — retrieving and placing it means walking in fast traffic on the hard shoulder. Use hazard lights, leave the vehicle by the left, and wait behind the barrier instead.
Walking with your back to traffic
People often stroll out to place the triangle without watching for oncoming cars. Always face the traffic as you walk back, so you can spot and dodge any vehicle that drifts towards you.
Out on the road
What this looks like in real life
Broken down on a country lane at dusk
Your car loses power and coasts onto the verge of a single-carriageway A-road just before a right-hand bend. You switch on your hazard lights first. Because the bend hides your car from approaching drivers, you don't stop at 45 metres — you walk back further, past the bend, facing the traffic, and set the triangle where drivers will see it in good time. Then you wait somewhere safe, well away from the road, and call for help.
A tempting but wrong motorway moment
You break down and manage to reach the hard shoulder of the M6. You've got a warning triangle in the boot and it feels like the responsible thing to set it up. Resist that instinct. On a motorway you leave it in the boot: walking down the hard shoulder in 70 mph traffic is exactly the danger the triangle is meant to prevent. Instead, switch on hazard lights, leave the car by the left-hand door, and wait behind the safety barrier while you call for assistance.
Quick answers
Frequently asked questions
Is it a legal requirement to carry a warning triangle in the UK?
No. Unlike many European countries, the UK does not legally require you to carry a warning triangle. However, it is strongly recommended, and if you drive abroad you may well be legally required to carry one, so many drivers keep one in the boot as a matter of habit.
How far behind the vehicle should I place a warning triangle?
On an ordinary road, place it at least 45 metres (147 feet) behind your vehicle, on the same side of the road. Increase that distance if you're near a bend or the brow of a hill, so drivers get more warning before they reach your stopped vehicle.
Why can't I use a warning triangle on a motorway?
Because placing and later retrieving it means walking a long distance along the hard shoulder in fast-moving traffic, which is extremely dangerous. On a motorway you should use your hazard warning lights instead, leave the vehicle by the left-hand side, and wait behind the safety barrier.
Do I still need hazard lights if I've set up a triangle?
Yes. The triangle and your hazard warning lights work together — the lights alert drivers who are already close, and the triangle gives earlier warning further back. Switch on your hazards as soon as you're stopped, before you deal with the triangle, and leave them on until help arrives.
Turn warning triangle rules into marks
Reading builds understanding — practice makes it stick. Pick up where this guide leaves off, free.
Revision checklist
0/6Tick each point once you can explain it without looking.