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Location Map ( geo)
Roosky - Coppermine - 16428.JPG
Cameraicon.png View gallery (98)
From:  Palmerstown (O080352)
To:  Sligo (G691367)
Distance:  198.2 km (123.2 miles)
Meets:  M50, R148, R113, R136, R835, R120, R148, R403, R449, R406, R158, R407, R159, R402, R401, M6, R446, R156, N52, R394, N55, R393, N63, R194, R198, N5, R371, R202, R201, R299, R280, R903, R368, R285, R294, N61, N17, R290, N59, R292, R287, R870, N15, N16
Highway Authorities

Transport Infrastructure Ireland

Traditional Counties

Dublin • Kildare • Leitrim • Longford • Meath • Roscommon • Sligo • Westmeath

Route outline (key)
N4 Dublin - M50
N4 M50 – Leixlip
M4 Leixlip – Kinnegad
N4 Kinnegad – Sligo

The N4 is the main route from Dublin, through the Irish Midlands, to Sligo.

The N4 is part of the NRA's 'East/West Corridor', making it a key priority for upgrades.


Like most roads radiating out of Dublin, the N4 today starts on the M50, as a high-speed grade-separated D3 bypass of Lucan. Beyond this, the road is D2M motorway standard as the M4, including a toll section, until just past Kinnegad. Some 8 km north-west of the split with the M6 the M4 ends and the dual carriageway resumes towards Mullingar. This section had grade turnings, but was upgraded with GSJs in 2013 and crossings of the central reservation were removed. This section joins the D2 Mullingar bypass, where there's a brief multiplex with the N52 around the town.

The start of the N4 Mullingar Bypass

The dual carriageway ends after Mullingar, and the N4 is back onto its original, single carriageway route past Lough Owel and up to Longford. There's then a single-carriageway bypass round the town, with a junction for the N5 at the end (having been bypassed in 2012), while the road turns more north to head along the various loughs that separate County Longford from County Roscommon. There is one section of reduced-standard dual carriageway heading into Carrick On Shannon, where the N4 crosses the river in the town centre.

The N4 then winds its way round Lough Key and Lough Arrow, where it enters County Sligo. From here, it's a reasonably straight run up to the N17, joining from the Atlantic Corridor, which is also the start of the Collooney Bypass. The N4 carries on along the bypass, which is dual-carriageway, to head towards Sligo, with the N59 coastal route joining in from the west.

The N4 through-passes Sligo itself and ends at a busy at-grade junction with the N15 and N16, with the old road, Barrack Street, joining in for good measure.


Dublin Port sign.
Coming into town along Conyngham Road.

The N4 originally started right in the centre of Dublin with the N1 and N11 at O'Connell Bridge. It ran along both banks of the River Liffey: until 1982 the north side was westbound only and the south side was eastbound only, and then with the opening of Frank Sherwin Bridge these swapped around.

Until then, the eastbound carriageway used Parkgate Street and Rory O'More Bridge (where it met the N7). The two carriageways then united to follow Conyngham Road out of the city, into Chapelizod.

Further changes came in 1987. From the newly re-arranged gyratory at the Liffey, the N4 moved onto St John's Road West past Heuston Station, the former N7. The opening of the Chapelizod Bypass had made it possible for the N4 to take this route past Palmerstown towards Lucan.

The old road through Chapelizod is now the R109, while the bypass itself has been downgraded to the R148 as far the M50. The R148 number is also used for the old, pre-M4 route west towards Mullingar.

Newcastle Road traffic lights.
The former traffic lights at Newcastle Road.

The N4 was chosen as the pilot road for Ireland's new road signs in 1977.

The current route of the N4 starts the 2009-rebuilt junction with the M50 and runs along a section of the 1984 Palmerstown Bypass, becoming the 1988 Lucan Bypass somewhat after Junction 2. This junction was constructed in 1997/8 replacing an at-grade junction with the Fonthill Road. The Lucan Bypass was widened in 2008/9 to D3 with a distributor road on parts of the Southern side, with the Newcastle Road junction being grade-separated, other median breaches (including a pedestrian one for the Spa Hotel) closed and some side roads closed or only accessible via the distributor road.

At Junction 5, the road becomes the M4 until Junction 13. The original route was via the town centres of Leixlip, Maynooth and Kilcock until the M4 opened in 1994. The road after Kilcock was of a very poor alignment until Enfield and was limited to well below the prevailing speed limits at the time. Enfield was bypassed in 2002, and the road from there to Kinnegad was then bypassed by the M4 in 2004.

After the end of the original 2004 M4, there was a section of HQDC N4 to link to the pre-existing DC. This section of HQDC was redesigned to M4 in 2009.

The Downs section was online dualled to a very poor standard in the late 1990s and was upgraded to near-HQDC standard by a 2012 grade-separation project. Mullingar was bypassed in 1995 with an almost HQDC standard road.

The road from Mullingar to Edgesworthstown has been extensively widened since the 1990s but is on its original alignment. Edgesworthstown was bypassed in 2006. A short section of mostly unmodified road links Edgeworthstown with the start of the 1995 WS2 Longford Bypass

After Longford the road is mostly unmodified until the start of the 2007 Dromod-Roosky T2DC bypass. This bypass was one of the pilot schemes for the new reduced-width DC standard which has now become the default for lower traffic dualling, featuring a barrier median, no hard shoulders and roundabout junctions. The road from here through Aghamore has been significantly widened but otherwise unmodified.

North of Aghamore, the 1996 Jamestown Drumsna bypass is a partially grade separated WS2 which runs almost to Carrick-on-Shannon. Through Carrick-on-Shannon, a mid 1980s "bypass" brings the N4 away from the town centre, but this has since become a further street for the town and does not function as a bypass.

After Carrick-on-Shannon, more on-line widening links to the mid 1990s WS2 Boyle Bypass, which itself runs directly on to the 1990s WS2 Curlews Bypass. Both of these schemes are very wide alignments and feature passing and climbing lanes. The Curlews are the mountain range here, rather than being a town name!

At the village of Castlebaldwin, a modern dual carriageway is reached. This was opened in 2021 and replaced the notorious section of the route between Castlebaldwin and Collooney.

A mostly HQDC bypass of Collooney and Ballysadare was built in 1998, beginning at the junction of the 1993 N17 bypass of the town, and running on the existing alignment before diverging to cross the Ownemore River via a new bridge. This originally ended at Carrowroe to the South of Sligo town centre, but was continued Northwards as HQDC until the edge of Sligo town in 2005, from where it continues as the at-grade dual Sligo Inner Relief Road until the end of the route. This Inner Relief Road had been proposed for decades and required significant demolition to achieve.

The original ending in Sligo ran along what is now the R287 and the R870, winding through the town core.

Future Projects

Planning and design work on 21km of T2DC from the existing T2DC Roosky Bypass to the WS2 Boyle bypass, bypassing Carrick-on-Shannon, began in 2019. It is likely that this will include online widening of the late 1990s partially grade separated WS2 Jamestown-Drumsna Bypass[1].

Design of 52km of mixed HQDC and T2DC between the existing HDQC Mullingar bypass and the T2DC Dromod-Roosky Bypass, bypassing multiple small towns and the existing S2 Longford bypass began in 2019. Much of this scheme will be online dualling of WS2 either built to new alignments or extensively widened in the 1990s[2].

It is eventually planned to online dual the Boyle and Curlews bypasses, which are currently WS2 with frequent passing lanes, to T2DC standard; completing DC the entire length of the N4.


Irish Statute Book

Irish Roads





Related Pictures
View gallery (98)
100 0774.JPGM50 J7 sw corner of roundabout - Coppermine - 12342.jpgRoosky - Coppermine - 16439.JPG05 Start Mullingar bypass - Coppermine - 6567.jpgR136 junction, R136 to right, N4 straight on. - Coppermine - 16076.JPG
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