31 people have lost their lives on the old stretch of road.
A new Sligo N4 dual carriageway from Castlebaldwin to Collooney has opened to traffic this week.
The 15km stretch of dual carriageway will replace the existing road and will be officially opened in September, however, it opened for traffic on Monday.
The completion of the N4 Collooney to Castlebaldwin Scheme was listed as one of the key things to be delivered under Strategic Outcome No 2 of the Enhanced Regional Accessibility of the National Development Plan (NDP).
This section of the N4 has been an accident blackspot for decades, with 31 people losing their lives on the stretch of road.
One of the largest road infrastructure projects in the country, it will reduce the travel time to and from Sligo, especially for those living and working in Boyle.
Construction on the mainline is substantially complete with snagging, fencing and safety works being completed at present.
However, Sligo County Council said some other works associated with the road will be ongoing until later this year but these will have minimal disruption to the N4 national road traffic.
Motorists are advised to exercise caution when using the new road until they become fully familiar with its layout and junction arrangements.
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