Red, White, Amber or Green? Reflective Road Studs Explained

One theory test question has been rising fast in UK Google searches this week: what colour are the reflective studs between a motorway and a slip road? It looks like a piece of trivia. It stops looking like trivia the first time you drive an unlit motorway at night, in rain, and the white lines have more or less vanished. At that point the studs are often the clearest thing telling you where you are.

The five colours and what they mark

Rule 132 of the Highway Code gives the full list, and it is short.

White studs mark the lanes or the middle of the road.

Red studs mark the left edge of the road.

Amber studs mark the central reservation of a dual carriageway or motorway.

Green studs mark the edge of the main carriageway at lay-bys and slip roads.

Green and yellow studs show a temporary change to the lane layout, for example where road works are taking place.

So the answer to the question everyone is searching is green. Where a slip road joins or leaves, the red edge line is broken and green studs take over for that stretch.

A simple way to picture it

Imagine you are in the left lane of a motorway at night. Red studs run along your left, at the edge of the carriageway. Amber studs run along the far right, beside the central barrier. White studs sit between the lanes. Wherever traffic can get on or off, the red on your left turns green.

If you like a hook, think of traffic lights. Red is the edge you should not cross. Amber sits next to the barrier and the oncoming traffic beyond it, so it is your warning side. Green is the gap where you are allowed to go, onto a slip road or into a lay-by. It is not a perfect match for what traffic lights mean, but it puts each colour in the right place, and that is all you need in the exam.

Why green is the one people forget

Red and amber are with you for mile after mile, so they stick. Green only appears for short stretches, which is exactly why learners mix it up. It is also the most useful one to know. On a dark motorway, a line of red studs switching to green is an early clue that a slip road is opening up on your left, sometimes before you have properly seen the exit.

It matters when joining too. The Highway Code motorway rules say you will normally join from a slip road on the left, and that you should stay on the slip road if it continues as an extra lane on the motorway. The green studs mark where that slip road meets the main carriageway.

Green and yellow: the road works colour

The fifth colour gets confused with plain green, but it means something quite different. Green and yellow studs tell you the lane layout has been changed for now, usually because of road works. In practice, treat them as a signal that the usual lines may not be where you should be driving: slow down and follow the temporary layout and signs.

How to make sure it sticks for the test

The question trending this week describes a location and asks for a colour. That is the useful way to revise it, because you can be asked from either direction. Grab a piece of paper and draw a quick cross-section of a motorway: barrier, lanes, edge, slip road. Then label the studs from memory. If you can do that in ten seconds without looking, you have it.

Studs are part of the same family as road markings and signs, which is one of the topics learners slip up on most. Our guide to road signs covers the shapes and colours of signs, and our post on clearways, red routes and yellow lines deals with the markings along the kerb.

Practise until it is automatic

Questions like this are easy marks once the picture is in your head, and annoying ones to lose if it is not. Theory Test Passed has the full DVSA licensed question bank, with explanations, so you can drill road markings alongside every other topic. Start at theorytestpassed.co.uk or download the app for iPhone or Android.