The Minister for Transport, Mr Cullen, turned the sod on the N52 Eastern By-Pass at Mullingar this morning.
The €20m project involves the building of 4.9 kilometres of single lane carriageway, four roundabouts, one railway crossing and one canal crossing.
The by-pass is expected to cut 20 minutes from peak-time journeys, and it is hoped to reduce by up to 60 per cent the number of vehicles travelling through Mullingar.
The project, funded by the taxpayer under the National Development Plan, should be finished in 2006.