The Newlands Cross flyover opened to traffic early this morning.
Officials on site planned the operation for 3am, allowing the first car to avoid the last remaining set of traffic-lights on the route between Cork and Newry.
National Roads Authority (NRA) spokesman Sean O'Neill said the early morning opening was to avoid potential problems that might occur had they opened it during busier traffic times.
The procedure, known as a “rolling stop”, meant on-site trucks with flashing lights bringing traffic to a gradual stop in two of the existing lanes and slowly funnelling it onto the new overpass.
The process was also overseen by gardaí.
“It’s the safest time to do it because there is less traffic. What you are doing is you are stopping the flow of traffic and redirecting it,” said Mr O’Neill.
There is still a couple of months of work ahead, with contractors returning borrowed land to a local golf course that had been used to accommodate diversions, as well as landscaping and the installation of signage and traffic lights for local access roads.
On budget
The 700m west Dublin project, which aims to eliminate one of the most notorious traffic bottlenecks in the State, was officially handed over by contractors Bam Civil, on budget and ahead of schedule, earlier this week.
The flyover will accommodate up to 90,000 vehicles each day over the Belgard Road and Fonthill Road.
The scheme will reduce journey times significantly for inter-urban and local motorists, particularly commuters from Co Kildare and beyond.
It comprises a two-span bridge structure with extensive approach embankments on the east and west sides of the junction.
It will have three traffic lanes in each direction.
The materials for the embankment were sourced locally and environmentally friendly cement was used to minimise CO2 emissions.
The junction is part of a public-private partnership project operated by Bam Contractors that includes building and maintaining the Arklow- to-Rathnew motorway in Co Wicklow.
The NRA has not disclosed the cost of the partnership but Bam Contractors’ website put the combined value of the Wicklow and Dublin elements at €126 million, without land costs.
The opening of the Newlands Cross junction was previously scheduled for spring 2015 but this was brought forward when better-than-expected progress was made.