The Minister for Transport, Mr Brennan, said the €192 million Ennis bypass was the first step in a western road corridor from Limerick to Tuam.
More than €35 million of this is required to pay for for design, planning and an additional €35 million is required for land purchase.
Mr Brennan turned the sod on the scheme this morning. When completed, the bypass will take 14,000 vehicles per day out of Ennis town, according to the Department of Transport.
Fourteen kilometres of dual carriageway will be built to form an eastern bypass. The contract includes a seven-kilometre relief road to the south and west of Ennis and 2.5 kilometres of dual carriageway from Killaw to Clareabbey and 4.6 kilometres of single carriageway to Claureen.
The project is scheduled to be finished in three years. The €119 million construction element of the contract has been awarded to multinational construction firm Gama Strabag Joint Venture.
Another element of the western corridor - the Crusheen/Gort bypass - is in the early design stage and that should be completed by the autumn.