Finished two months ahead of schedule, the 5.4km roadway will ease the flow of traffic into Kerry from the Limerick-Dublin side and is expected to improve journey times by up to 30 minutes at peak periods.
The bypass will divert 60% of all traffic and up to 80% of heavy goods vehicles from the town and should also boost business in Castleisland due to easier access.
It also includes 3km of dual carriageway, with a wire barrier running along the centre, which has been shown to significantly reduce the severity of collisions and fatalities.
However, Defence Minister Tony Killeen, who performed the opening, said that did not reduce a driver’s responsibility to road safety and preventing accidents.
He also said the bypass would create major opportunities for business and development in Castleisland in the absence of daily traffic jams and lack of parking facilities.
“The pattern of bypassed towns flourishing in the absence of choking traffic is one that can be witnessed all across the state in places like Naas, Gorey and elsewhere. These towns have grabbed this golden opportunity with both hands and have thrived,” Mr Killeen added.
National Roads Authority chief executive Fred Barry said the Castleisland bypass had very strong community support and added that the next big road project in Kerry, the Tralee bypass, had gone to tender.
It was the NRA’s intention to start construction work on the Tralee bypass, early in 2011, he pledged.
Kerry county manager Tom Curran welcomed Mr Barry’s statement on the Tralee bypass, but stressed major improvements were still needed on major roads leading to Co Kerry.
He mentioned, in particular, the Adare to Abbeyfeale road, in Co Limerick, and the Ballincollig to Ballyvourney road, in Co Cork.
Mr Curran told how, earlier in the week, a journey from Cork to Tralee took much longer than expected for a senior EU official who remarked to him “the route is very pretty, but hell to drive on”.
Construction work on the Castleisland bypass by Bam Civil Engineering began in May 2009.
The bypass skirts Castleisland town on the western side and links the Limerick, Tralee and Killarney roads.