The 3km bypass around Edgeworthstown, Co Longford, has been completed.
Work on the relief road began in June 2005 and, according to the National Roads Authority (NRA), was expected to open in the second quarter of this year.
A spokeswoman for Longford County Council said the council was aiming to have the road open by June 19th.
The scheme is a single carriageway road through undeveloped land to the south of the town. It incorporates two roundabout junctions, one at the eastern end and one roughly in the middle where the bypass crosses the Athlone-Edgeworthstown road. It includes "a minor bridge structure" over the Black river.
A spokesman for the NRA has acknowledged that the construction time was longer than usual but added that it would be a "first-class road" built by a local contractor.
"It is only a little road but it will take 70 per cent of the traffic out of Edgeworthstown" he said.
A county council spokesman said there had been extensive work in tying in the bypass with the existing N4 east of Edgeworthstown, which had been time-consuming.
Although it was a greenfield site, this end of the route was "more of an urban environment", he said.
While the travel time between Dublin and Sligo has been considerably reduced in recent years, Edgeworthstown remains the last major bottleneck on the N4, following the opening of the new toll motorway to Kinnegad earlier this year.
Bypasses of Longford town on the N4 west of Edgeworthstown and Mullingar to the east have been open for about a decade.
Traffic through Edgeworthstown, which is a main artery between Sligo, Mayo, Longford and Leitrim, increases significantly at weekends when tailbacks can stretch for about a mile outside the town and delays of up to half an hour can be expected either side of the town.
With a construction time of just 3km a year, the road was still completed in a faster timeframe than Dublin's 41km M50, which was constructed at roughly 2km a year over 20 years.
In contrast, the Kilcock/Kinnegad motorway in the midlands, which is also 40km long, was built in about 27 months.
Meanwhile Minister for Environment Dick Roche is to officially open the Greystones Southern Access Route in Co Wicklow later this month. The four-lane dual carriageway which forms a bypass of Delgany village has now been linked to the N11 by a single carriageway road of about half a kilometre.
