Explanation

"Reflective studs are placed along the edges and between the lanes on motorways. The colour of the stud can help you identify your position on the road when visibility is reduced; for example, when it's foggy. Between the lanes, the studs are white. Red studs are used between the left-hand edge of the carriageway and the hard shoulder. Amber studs are used along the right-hand edge of the carriageway, and green studs are used where slip roads enter or leave the motorway."