Irish Rail inspected and passed a section of rail track as safe just a day before it was submerged after trains went over it.
It has been revealed that the stretch of line north of Dublin was approved by two Irish Rail inspections in the days before it sank into the water on Friday.
The first inspection was carried out by an Irish Rail engineer on Tuesday and the second survey was undertaken by a track-recording vehicle the day before the incident.
But Irish Rail last night resisted calls from an environmental group and construction employers to immediately initiate a national survey of bridges along its network.
It said it would await the outcome of its investigation into last week's incident as the circumstances surrounding the collapse may have been unique to that stretch of track.
The track collapse could have been disastrous as a packed train from Balbriggan to Dublin city centre had just passed over it before it sank towards the water around 6.25pm.
A spokesman for Irish Rail said the first inspection was a visual inspection, which are carried out on an ad hoc basis.
He said bridges on the network were fully inspected every two years. Tuesday's inspection was not a full one but was used to assess whether markings or cracks were of a structural or cosmetic nature.
The second investigation last Thursday by a track recording vehicle, which take place every six months, would have measured any differences in levels and even minor subsidence.
“Even if the level differences were minuscule, it would have picked it up,” said the spokesman.
“There is no point jumping to conclusions until the investigation is complete,” he said.
He added that ongoing inspections of bridges across the network would continue.
The Construction Industry Federation called for an immediate assessment of all bridges used by Irish Rail. Don O'Sullivan of the federation said the cost of repair could range from €1m to €25m.
Damien Cassidy of the National Conservation and Heritage Group said that a national survey of bridges was urgently needed “because people are going to get killed”.