What do blue circular road signs mean in Northern Ireland?

Blue circular signs generally give positive instructions or indicate a mandatory route or movement.

They can require a particular direction, route, lane or class of traffic to follow the instruction shown. Blue does not mean the sign is optional.

For “What do blue circular road signs mean in Northern Ireland?”, the wider Northern Ireland context is this: Northern Ireland's Highway Code uses signs, signals and road markings together, so the safest reading is always the exact sign at the location plus any lane arrows, plates or temporary traffic management. Rules expressed as ‘must’ or ‘must not’ are legal requirements; advisory wording can still be used as evidence when responsibility for a collision is considered.

For this exact question — “What do blue circular road signs mean in Northern Ireland?” — the practical point is: Read the symbol carefully and follow the direction it gives; check nearby lane markings because the sign may apply only to a specific lane or approach. The answer should be applied to the actual signs, conditions, licence wording or parking rules in force at the time, because temporary restrictions and individual DVA decisions can change the ordinary position.

This Northern Ireland-specific page on “What do blue circular road signs mean in Northern Ireland?” was checked against the attached official sources before publication, with nidirect/DVA and the Northern Ireland Highway Code used ahead of generic UK motoring articles. If the rule, road layout or personal licence condition changes, those primary sources are the ones to re-check.