The €148 million Ashford to Rathnew bypass in Co Wicklow has been formally opened by the Minister for Transport.
The bypass, which currently caters for an average of 20,000 vehicles per day, extends the Dublin-Wicklow motorway to 50 kilometres.
Mr Brennan said that the new road, which was completed five months ahead of schedule, would bring enormous benefits to motorists and other road users as tailbacks and delays, sometimes of up to an hour or more, are replaced by free-flowing traffic conditions.
"There will also be substantial economic benefits as access to and from Dublin to the south east and the south will be speeded up, and those using the north/south corridor will have reduced journey times," he said.