AAATHE used on wide carriageways to divide them into lanes. You should  keep between them.  132. Reflective road studs   may be used with white lines.  ● 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/yellow studs indicate temporary adjustments to lane  layouts, e.g. where road works are taking place.  highwaycodeuk.co.uk 71 