Defects in the timber deck structure of Cahir Viaduct and in Iarnród Éireann's inspection and maintenance regime were "principally responsible" for the viaduct's collapse following the derailment of a freight train in October 2003.
"If these had been fit for the purpose, it is unlikely that an accident would have occurred," according to the Railway Safety Commission. Its report on the accident also concluded that trains crossing the viaduct "may have been at risk of derailment for some time prior to the accident".
It said there was "almost certainly" a significant risk to some of the 15 trains that crossed the viaduct in Co Tipperary after maintenance works were completed on the Sunday before the accident. "This included two passenger trains," the 72-page report said. "If appropriate standards and specifications had existed at the time of the accident and had been rigorously applied in relation to the design, inspection and maintenance of the viaduct, it is unlikely that the derailment would have occurred."
The accident occurred when a cement train from Limerick derailed on the viaduct, causing it to split apart. Twelve wagons fell through the bridge into the River Suir, 15 metres below, while two engines and the first 10 wagons of the train remained on the track.
Although nobody was injured in the early morning accident, damage to the railway and the freight train cost more than €3 million to repair. This included an underwater survey to locate debris and the removal of cement wagons from the river to prevent pollution.
The commission noted that the train was travelling at 69km/h, 5km/h faster than the speed limit for the line between Limerick Junction and Rosslare, but it said that this was not the primary cause of the derailment and bridge collapse.
"The train speed may have contributed to the extent of revealing a critical fault in the track, but it can be ruled out as a cause . . . The construction of the cement wagons made them more sensitive to track irregularities than bogie wagons, but laden cement wagons rarely derail. The train had successfully passed through a number of locations where the ballast track was in poor condition. However, failure to maintain track parameters is more critical on way-beam structures, which are more rigid and less forgiving than ballast track."
In reporting the accident, the driver said he was unable to make use of the train radio as the train was in a reception "black spot". Though the time lost was not critical, "had anyone been injured as a result of the accident it might well have been so", it said.
A new railway patrolling standard with revised reporting and signing-off arrangements had been in course of development for about two years prior to the accident, but its implementation only started a month afterwards.
The report makes 15 recommendations. These include a review by Iarnród Éireann of its safety management and communications systems, monitoring adherence to speed limits and ongoing track monitoring.