The National Roads Authority (NRA) is to prioritise a feasibility study into an outer orbital route for Dublin.
The study is expected to feed into a decision by the Government next year on whether to proceed with the the road, which the Taoiseach, Mr Ahern, has previously indicated that he favoured.
Experts will provide detailed costings to the Minister for Transport, Mr Cullen, on a route from Drogheda, through to Navan and on to Naas.
However, it will not be completed in time for detailed proposals to be included in a presentation by Mr Cullen to Government colleagues next month on a 10-year transport plan.
If the Government decides to proceed with the road, which is likely to cost over €1 billion, the detailed design and planning process is likely to take at least three years before construction can begin.
The outer orbital is being seen as increasingly likely with capacity problems continuing on the M50.
While a planned €800 million upgrade of the M50 to three lanes will begin next year, it will alleviate congestion for a limited period. Traffic projections show the upgraded road reaching capacity by 2015.
Announcing the feasibility study yesterday, Mr Cullen said that outer ring road "will not happen overnight".
"Now is the time to explore how it could work, the difference it could make and how much it would cost."
Mr Cullen and the NRA also rejected suggestions from opposition parties that the announcement of the feasibility study was linked to the Meath and North Kildare by-elections.
The road, if built, would pass through both of these constituencies, where traffic congestion is a major issue.
"I never put it in that context at all," said Mr Cullen.
Mr Michael Egan, of the NRA, said there was "nothing new" in the proposals, which the authority had been discussing with the Minister for some time.
"Clearly we have to be able to plan for the future, and this project has been well flagged in publications like the Dublin Transportation Strategy. It's not something we've just pulled out of a hat."
Meanwhile the Department of Transport is to draw up legislation to allow for the introduction of electronic tolling on Irish roads.
The system will lead to the lifting of barriers on the M50, which have been blamed for contributing to gridlock.
The NRA said yesterday it was in discussions with National Toll Roads (NTR), the owner of the West-Link bridge, with a view to lifting the barriers by 2008.
NRA officials said primary legislation was needed to enable NTR to pursue toll evaders to make the electronic system workable.
The system would rely on electronic chips in cars which could be read as they passed by the toll booth.
The authority is also developing proposals for a central tolling system, whereby motorists could be billed on a monthly basis for various toll charges they incurred.