The A3 becomes the N12 between Armagh and Monaghan
The N12 is one of the shortest National Primary roads. It starts on the N2 Monaghan Bypass and heads off in a northeastly direction, roughly following the line of the River Blackwater. Less than 7 km later, it crosses the border into County Armagh and becomes the A3.
Before National Primary Roads were introduced in 1977, the N12 was the T15. The allocation of such an important number to such a short road is easily explained by the wider picture in which it forms, in combination with the A3 and A1, part of a strategic route from Monaghan to Armagh, Lisburn, and Belfast.