Metro North could be finally scrapped as a result of alternative transport options for north Dublin being considered by the Government.
Minister for Transport Pascal Donohoe announced six options proposed by the National Transport Authority that would be ready to connect Dublin Airport and Swords to the city centre in seven to ten years time.
A new Metro North plan is being considered, but Mr Donohoe said the original Metro North plan was "clearly a project of its time" and mistakes had been made in terms of projected population growth.
The population increase in Fingal had been 22% in the five years up to 2006, but slowed to 14% over the following five years.
A number of other options are being considered, including link ups with DART, with the new Cross City Luas, with mainline railway or a series of enhanced bus routes.
Mr Donohoe said the public transport needs of north Dublin are not being met where the population growth is still four times that of Dublin city centre and twice that of other Dublin council areas.
He also said that if the current growth in car usage continued there would be additional 40,000 cars coming into Dublin city centre by 2023 which would require 40 new multi-storey car parks in the city centre.
Mr Donohoe said "that cannot happen."
The scaled down Metro North would have fewer stations, travel at ground level in Ballymun and would cost up to €2.8bn - €460 million less than the original plan.
Then there is a proposal for a DART link from the Maynooth railway line at Drumcondra via a tunnel under Glasnevin which would cost € 2.1bn.
There is also an option for a link or 'spur' from the DART line at Clongriffin that would cost €790m.
Another is a Luas line from the future Cabra Luas station and going through a tunnel under Glasnevin which would cost just over €1bn.
There is also a combination of a Luas from Cabra to Swords and a DART from Clongriffin to the Airport which would cost up to €1.3bn.
A series of Bus Rapid Transit routes to service the area would cost €570m.
Members of the public are being invited to make submissions on their preferred option by 19 January with the Minister due to make a decision on the final option in June.
He will also be considering a new business case for the Underground DART project in the city centre.
The option for using the Phoenix Park rail tunnel as a link to Swords and the Airport was rejected on a number of grounds including the belief that its success would depend on the Underground DART being completed and connecting at Heuston Station.