From Longford, the N5 passes through Strokestown and close to Ballaghaderreen, before crossing the N17 at an interchange near Ireland West Airport and continuing westward to bypass Swinford and Castlebar before terminating in Westport.

The remainder of the route – between Frenchpark and Strokestown – consists of a narrow road with no hard shoulders, and with a poor horizontal and vertical alignment allowing few overtaking opportunities.

Political arguments were given more weight in recent years when several major multinational firms based in Mayo joined forces to lobby the government to upgrade the N5.

This scheme comprises 13.6 km (8.5 mi) of standard single carriageway and provides a bypass to the north of Ballaghaderreen town.

Transport Minister Leo Varadkar turned the first sod on the project on 2 November 2012, and the road was opened on 2 September 2014 by Taoiseach Enda Kenny.

It is named the John Healy Road in honour of the late Irish Times journalist who wrote about the economic decline of Charlestown in the 1960s.

An 8 km (5 mi) stretch of standard single carriageway between Strokestown and Longford commenced construction in September 2001 and was officially opened on 10 May 2004 at a cost of €21 million.

The singer Ronan Keating's brother was killed in one of the numerous fatal collisions along this part of the N5, leading to repeated calls from the Mayo county coroner for safety improvements to be made.

[2] This 10 km (6.2 mi) single carriageway includes a bypass of Turlough village and a relief road around Castlebar which opened in 1990.

The western end of this scheme, including the Castlebar relief road, was itself bypassed and redesignated as the R309 after the 2023 opening of the Turlough to Westport dual-carriageway.

[9] The project involves the upgrade of the N5 in County Roscommon between Rathkeery at the eastern end of the Ballaghaderreen bypass and Scramoge, east of Strokestown.

Approximately 8 km (5.0 mi) west of the town, the N5 crosses the River Shannon into County Roscommon at Tarmonbarry Bridge.