The Minister for Transport has opened the new Limerick southern ring road.
The 9.5 kilometres of dual carriageway cost €106 million and is expected to divert more than 10,000 vehicles a day from the city and cut travel times from Dublin to Cork
Mr Brennan said a further eight kilometres of national primary single carriageway and local roads will also be opened today.
"This road scheme will boost economic development and expand regional development in the West and South," Mr Brennan said.
"More and improved infrastructure is a cornerstone of future growth. Limerick is a vibrant and expanding city and by filtering a large volume of traffic away from the centre of the city, the Southern Ring Road Phase 1 will have a big impact on alleviating congestion and improving safety in the city."
Mr Peter Malone, chairman of the National Roads Authority, said the body had allocated €150 million to the N7 this year in order to advance road building schemes.
The final phase of the southern ring road, which will incorporate a fourth crossing of the River Shannon, will take four years to build.
An Bord Pleánala recently held an oral hearing into the compulsory purchase order and Environmental Impact Statement for the second phase of the road and a decision is pending.