A planning hearing for Dublin's proposed underground DART got under way this morning to consider 287 objections and submissions.
Irish Rail said the link would treble the number of passengers but questions have been raised about the cost, which is estimated to be at least €1.3 billion.
The 7.6km tunnel would link the docklands to Heuston station with stops at Pearse St, St Stephen's Green and Christchurch, while an overground line would continue to Inchicore.
If An Bord Pleanála grants permission, Irish Rail hopes to start work in 2012 and complete the line by 2018.
It would link the existing DART line with LUAS, Commuter and Intercity lines as well as the planned Metro North and increase rail passenger numbers from 33 million a year to 100 million.
Irish Rail also says that the project's economic benefit to the country will be 2.4 times the cost and create 7,000 jobs.
The company has decided to use two boring machines instead of four to save cost and has moved most of the tunnel boring from Inchicore, where it could cause structural damage, to the company's property in East Wall.
But residents of East Wall claim the works will turn their area into a massive excavation and mining pit for the best part of a decade.
Residents' spokeswoman Angela Broderick also objected to the fact that the hearing is being held in Tallaght, 15kms from East Wall.
Lawyers for property developer Owen O'Callaghan are also contesting the jurisdiction of the hearing claiming the project will 'sterilise' his lands, which include the Davenport and Alexandra Hotels.
Private members' clubs in St Stephen's Green, Diageo and Bank of Scotland Ireland are among a number of city centre organisations also due to make submissions to the hearing, which is due to last a number of weeks.
Residents' groups in East Wall and the Pearse St area will also be making submissions.
