M4 motorway (Republic of Ireland)

The M4 by Leixlip

The M4 motorway is a motorway section of the N4 road, a national primary road in the Republic of Ireland, running from Dublin north-westwards to Sligo town. The M6 to Galway diverges from the N4 route after Kinnegad, while the N5 to Westport diverges at Longford town.

The motorway section runs from Leixlip to the west of Kinnega. The first section of this motorway (Leixlip – Kilcock) was opened on 19 December 1994.

Tolled section of the M4 motorway

The motorway was announced in 1999: the project involved the construction of 24 miles of motorway from Kinnegad to Kilcock and is an extension of the Kilcock-Maynooth-Leixlip motorway on the N4 Sligo/Galway to Dublin route. The motorway bypasses the towns of Enfield and Kinnegad.

The tolled section (from Kilcock to Kinnegad) opened on 12 December 2005, almost a year ahead of schedule. It is the most expensive toll road in Ireland after the Dublin Port Tunnel. A toll of €3.50 (as of 2025) for cars is charged at a toll plaza just west of Kilcock and at smaller toll plazas at on and off-ramps at Enfield. Between Enfield and Kinnegad, no further access to the M4 is possible.

In the 1 July 2006 edition of the Meath Chronicle it was claimed that up to 10% of the €420 million road project had "to be ripped up and replaced" shortly after it opened due to rushed construction, however this cost would have had to be carried by the toll operators, not the state, as per the contract.

The bypassed former N4 road has been reclassified as the R148.

Motorway reclassification

On 28 August 2009, the Department of Transport implemented the second round of proposed reclassifications of dual carriageways as motorways. A short section of the N4 between Kinnegad (J12) and McNead's Bridge (J13) was affected by this, extending the M4 westward by 4.2 miles.

Junctions

The route begins as a dual carriageway at junction 7 of the M50, becoming a motorway after junction 5. It then becomes a dual carriageway after junction 13. After Mullingar, it becomes a regular national primary road.

County	km	mi	Junction	Destinations	Notes
County Dublin
			1	– Dublin Airport, Dublin Port, Dún Laoghaire	Continues as R148 towards Dublin city centre and Palmerstown.
			2	‒ Fonthill, Liffey Valley
			2a	Ballyowen Lane	Westbound exit only. Exit lane runs parallel to mainline, ending at slip road at junction 3.
			3	– Ballyowen, Lucan
			4	– Lucan, Adamstown
			4a	L1018 – Dodsboro, Kew Park	Only Dodsboro is signposted on eastbound approach. Exit lane runs parallel to mainline, ending at slip road at junction 5.
			5	– Celbridge, Leixlip (westbound)	Heading eastbound, both destinations are followed by 'East' Continues as M4 motorway.
County Kildare
			6	‒ Celbridge (West), Leixlip (West)	Dunboyne
			7	‒ Maynooth, Naas	Straffan
			8	‒ Kilcock  – Clane	Enfield, Trim
			M4 Toll
			9	‒ Edenderry, Enfield	Toll at westbound entrance and eastbound exit slip roads.
County Kildare			Enfield Service Area
County Meath			10	‒ Kinnegad
County Westmeath			11	‒ Galway, Athlone	Tullamore (N52)
			12	‒ Kinnegad, Galway (M6)	Westbound entrance and eastbound exit only.
			13	L1025 ‒ Coralstown	'LILO' junction. Continues as N4 dual carriageway.
			14	‒ Killucan, The Downs
				L5720	LILO junction. Westbound entrance and eastbound exit only.
			15	‒ Tullamore, Mullingar (East)
			16	‒ Dundalk, Mullingar (Centre)
			17	‒ Castlepollard, Mullingar (West)	Mullingar Hospital Continues as N4 regular national road.