National primary road

The routes numbered N1–N11 radiate anti-clockwise from Dublin, with those in the range N12–N26 being cross-country roads.

Finally, the N40 and the M50 are bypass roads of Ireland's two largest cities, Cork and Dublin.

Signs for roads of a different standard are shown using appropriately coloured patches according to a system derived from the UK's Guildford Rules.

Sections of some national primary roads form part of the European route (E-route) network.

E-route numbers are placed on some route confirmation signs on certain sections of these roads.

[4] The N32, which had been constructed from new as an extension of the M50 Northern Cross Route project became part of the system in 1996.

These roads have at least two lanes in each direction, an unbroken central median, and access only at special interchanges.

A high-quality dual carriageway may be redesignated as a motorway by means of an order under the Roads Act 2007.

In addition to the major interurbans, the N11, N17, N18, N20, N21, and N25 – all of which form links between regional cities or other strategic links – also have major sections of good standard dual carriageway (in the N18's case, the entire route is made up of dual carriageway and motorway since 2017), with some sections of motorway also in place.

[5] Based on the combined lengths of existing roads, current construction and proposed future construction, it is probable that over 50% of the national primary road network will be either motorway, high-quality dual carriageway or 2+2 dual-carriageway by 2030.