The A509 and A46 roads in Northern Ireland form part of an overall route connecting to Enniskillen, and northwest to the border again where the N3 reappears to serve Ballyshannon in County Donegal.

Rush hour congestion between Navan and Dublin city was very heavy (up to 22,000 vehicles per day on single carriageway portions of the N3 in 2002), and problems occurred at most built-up areas between these points.

During The Troubles in Northern Ireland, the border crossing at Aghalane Bridge, which spanned the Woodford River just north of Belturbet, was closed.

[1] The National Roads Authority in conjunction with Cavan and Donegal County Councils plan major improvements to the N3 route in Ulster.

The motorway was contested because the route passes near the Hill of Tara and through the archaeologically rich Tara-Skryne valley or Gabhra.

A short section of the existing dual-carriageway N3 bypassing Clonee, from northwest of Mulhuddart to the start of the M3 toll motorway scheme, is affected by this.

Following a public consultation process, on 10 July 2009 the Minister for Transport, Noel Dempsey, made a Statutory Instrument reclassifying this section of the N3 as motorway effective from 28 August 2009.