DISRUPTION on a "massive" and "inconceivable" scale would be caused to city centre streets, including Grafton Street and College Green, if critics of the £220 million light rail transit (LRT) project succeeded in forcing it underground, according to a major report.
Commissioned by CIE's light rail project team, the report examines a number of alternatives to LRT, including DART style regional express trains, trolley buses, monorail and subway systems. But its most startling findings relate to putting LRT underground.
This option has been promoted by Dr Garret FitzGerald, in his series of articles in The Irish Times last week, and others, notably Senator David Norris, to avoid on street LRT creating congestion because of the closure of important links such as Nassau Street to ordinary traffic.
The report, by consultants Semaly/EPO, who are advising CIE on its plans, says the construction of a short underground link between Westmoreland Street and St Stephen's Green, as some of the critics have suggested, would close Grafton Street for at least a year.
Discounting the notion that it is possible to build tunnels with no impact on the surface, the report explains that this option would involve digging a trench, 26ft wide and 26ft deep, along the entire length of the proposed tunnel, causing "massive disruption" to streets.
"It's absolutely horrific what would be involved," said Mr Donal Mangan, director of the LRT project team and chief executive of Dublin Bus. He pointed to pictures from the French city of Lyons to show the reality of tunnelling through a city centre.
"Technically speaking everything is possible," said Mr Jacques Bourreau, of Semaly, who is from Lyons. "But when I hear people suggesting that, with an underground system, there will be no disruption to the town well, they are absolutely wrong.
Even a medium length underground system, designed to avoid the city centre, would also be "extremely disruptive" to the areas affected by tunnelling. The additional cost "would be in the order of an extra £120 million", more than half as much again as the LRT estimate.
This scenario would involve taking the Tallaght line underground at Benburb Street, running into the city centre and emerging to the surface again at Adelaide Road on the Dundrum route. Much of the disruption in this proposal would involve extensive excavations for stations.
Referring to the much canvassed Unified Proposal, which would put the LRT network underground inside the canal ring, the report says it was "extremely difficult" to evaluate as it had not been "fully thought out" and was "seriously deficient" at a technical level.
"However, based on the limited information available, a reasonable cost of the proposed system (put forward by two engineers, Mr Cormac Rabbit and Mr Rudi Monahan) would be in the order of £460 million", more than double the budget currently available for LRT.
A recent four hour meeting between Mr Mangan, his LRT consultants and the Unified Proposal promoters failed to resolve the issues between them. "We got no satisfactory answers, for example, on where they would excavate for their central station in Temple Bar," he said.
Mr Aengus O hEocha, of EPO, pointed out that his firm had designed over 5,000 kilometres of tunnels worldwide, including the Lee Tunnel in Cork, whereas the promoters of the Unified Proposal, which relies so heavily on tunnelling, had designed "zilch".
Mr Bourreau said it was "nearly impossible" to give accurate cost estimates for tunnelling because of the uncertainty about geological conditions. "The tunnel boring machine in Lyons, for example, was stopped for six months because of unforeseen problems."
Detailing the environmental impact of going underground in the city centre, the consultants say the continuous nature of tunnelling would require a 24 hour operation, "with noise and vehicle movements, including heavy goods vehicles, at all times during the day and night".
Substantials areas would be needed for construction sites, possibly in sensitive parts of the city centre, the report says. Occupants of adjacent buildings would be exposed to noise and dust, while ground movements could undermine their foundations by causing "differential settlement".
Considerable traffic management would be required to control vehicle movements in the affected areas, including heavy goods vehicles carrying concrete materials for tunnel linings and removing spoil from the excavations.
For "cut and cover" tunnelling, environmental conditions in adjacent properties would be extremely poor, the report says. "Noise, dust and vehicular intrusion would be substantial ... and, even after the roof was cast, the nuisance would be focused on the work sites at either end."
Since "cut and cover" would have to be used because of the relatively short distance of one kilometre between Westmoreland Street and St Stephen's Green this would mean the excavation of a continuous trench during the construction period, which would extend over a year.
"It is clear that the construction of cut and cover structures and transition structures (the gradients at both ends, each of which would be some 120 metres long) would ... be 50 disruptive and have such adverse impacts that it will be unacceptable to the public.
"To consider putting such a tunnel through Grafton Street raises many technical questions including the width of the street and the capability of the existing buildings to withstand ground movements, let alone the economic impact on the retailers," the consultants say.
Drilling and blasting for a longer bored tunnel through the limestone calp under the city centre could also adversely affect adjacent properties. It would involve "more coming and going, noise, lighting and removal of spoil/delivery of materials than with cut and cover".
Mr Bourreau said there was no attempt to hide the fact that installing on street LRT would also involve disruption. However, at any given time this would only affect a section of street amounting to 200 to 300 metres "because if it was longer than that, we know the city cannot work".
The consultants conclude that on street LRT is "the correct technology for Dublin" because it would provide a high quality public transport system with the ability to expand capacity as demand grows as well as enhancing the attractiveness of the city, particularly for pedestrians.
They describe LRT as "a tool to help reclaim city streets from the car" because it is designed to run on street, displacing existing private car traffic. "A subway type system has no impact on the streets, which will continue to be filled with cars unless other measures are taken."
However, Mr Mangan emphasised that elaborate computer modelling had shown that LRT would not create the gridlock" predicted by some of its critics. "The system will work. The city will work. And the traffic will flow, despite what Garret FitzGerald says."
