The benefits of the proposed upgrading of the M50 motorway could be diminished if a superstore development in north Dublin goes ahead, according to the National Roads Authority.
Mr Michael Egan, head of corporate affairs at the NRA, said any planning application facilitated by the Government's decision to remove a cap on the size of stores would have to be judged on its own merits.
However, were a development like that proposed in Ballymun to proceed, "we would be insisting on a specific traffic impact assessment".
The NRA is planning a €810 million upgrading of the M50, which would see a 19 per cent improvement in traffic flow by 2008, falling to 11 per cent by 2023.
If the suggested Ballymun plan went ahead, "we might face a shortening of the better performance that we expect from the upgrade", Mr Egan said.
"We can't contemplate a situation where we freeze development because there is a finite capacity on the M50."
But nor, he said, would the authority allow significant investment in infrastructure to be "frittered away on a willy-nilly basis".
A Bord Pleanála hearing on the M50 upgrade resumes next Tuesday.
The Dublin Chamber of Commerce also warned about the possible traffic implications from the introduction of new superstores.
Ms Gina Quin, the chamber's chief executive, said that, while the organisation welcomed the lifting of the planning cap, recent developments had shown the negative consequences for traffic of locating major retail developments near the M50.
Further developments would only serve to exacerbate congestion levels along the city's orbital motorway.
She added: "These large retail warehouses should be the exception and not the norm for development of retail in Dublin."
The Swedish furniture group Ikea, which has indicated plans to establish its first Irish outlet at Ballymun, next to the M50, yesterday publicly welcomed the lifting of the cap, saying it allowed Ikea to review opportunities to enter the Irish market.
In a statement the company added: "This decision by the Irish Government reflects recognition of the need to widen consumer choice by bringing greater competition into the Irish retail market plus the regeneration benefits that companies like Ikea can bring to areas of urban renewal in Ireland."
The US warehouse giant, Costco, and the B&Q do-it-yourself chain have also expressed interest in developing warehouse superstores in Ireland.
Domestic retailers have given a mixed reaction to the move.
The east coast furniture chain, Living, said it would welcome the competition, given that people were going to Scotland "in their droves" to buy from retailers such as Ikea.
