A third toll bridge across the Liffey in Dublin has been sanctioned by the Minister for the Environment, Mr Dempsey.
He has also given the go-ahead to a £90 million bypass of Monasterevin, which will help to remove major bottlenecks on the main Dublin-Cork-Limerick route.
The new toll bridge will be east of the existing West Link Bridge on the M50 and will be financed under a public-private agreement between the National Roads Authority and National Toll Roads Ltd.
However, Opposition parties have condemned the Dublin decision and said any move on the toll bridge should wait until the Flood tribunal is concluded.
Ms Joan Burton, a former Labour minister of State and a councillor, criticised the Minister for waiting "until the last working day of the year" to announce what she described as the first public-private partnership of the new National Plan.
She also asked why there had been no public tender for the second toll bridge and said it was unjustified that a "licence to print money" was granted to NTR while the Flood inquiry was still in train.
"National Toll Roads, as the promoters of the first toll bridge, were allowed the exclusive right to this further licence at the time of the initial agreement," she said.
"NTR has also featured in the evidence to the Flood tribunal in relation to payments to both Mr George Redmond and Deputy Liam Lawlor. Indeed, Mr Lawlor in his recent session in the witness box has suggested that £74,000 was paid by NTR to him as a political donation," she added.
The Green Party also sharply criticised the decision and said the Minister was "riding roughshod" over local opinion. Mr Paul Gogarty, a councillor, said it would cause untold damage to the quality of life of Palmerstown residents.
The Minister was unwise to announce the bridge when "questions about the granting of permission for the first one may yet have to be investigated by the Flood tribunal". He urged the Minister not to proceed until the issue was clarified.
Mr Dempsey, making the announcement, said both projects would be a major boost to the country's infrastructure and of particular benefit to motorists travelling between Dublin and Cork and Limerick.
The new bypass will link up with the existing Portlaoise bypass east of that town, and connect with the proposed Kildare town bypass to the east of Monasterevin. It will enable a continuous motorway network to be put in place, linking the N7 and N8 to the south of Portlaoise with Naas, and to connect with the Naas dual carriageway which provides access to the M50 around Dublin. The National Roads Authority expects work to start on the bypass this year.
The proposed £18 million third toll bridge across the Liffey will be 385 metres in length and similar to the existing West Link Bridge, apart from the configuration of its piers. "It will go a long way towards doubling peak-time capacity on the M50 and ending congestion on this crucially important motorway link," the Minister said.