An estimated 20,000 cars and trucks will bypass a number of well-known accident blackspots as a result of the opening of the Birdhill to Limerick section of the M7 motorway.
The section between Nenagh and Limerick was originally due to open last year, but the project was delayed because of subsidence on a stretch of road through Annaholty bog.
Transport Minister Noel Dempsey said the opening of the new section at Birdhill will remove high volumes of traffic from serious accident locations like Daly's Cross and Yellow Bridge and improve road safety for all motorists.
It is expected that journey times between Nenagh and Limerick will be reduced by ten minutes initially.
Journey times to Dublin will be reduced further when the final section of the M7 from Castletown in Co Laois to Nenagh, which will bypass Roscrea, Moneygall and Toomevara, will be completed by the end of the year.
Work started on the 12.5km section in 2006. It was originally scheduled to open in May 2009.
The problem was caused by the failure of supports driven into the bog on which the road was constructed.
As a result, a 100m section had to be excavated and rebuilt from scratch.
Extensive load testing has been carried out in recent months to ensure the road is fit for purpose.
The final section of the motorway between Castletown and Nenagh will be finished by the end of the year.