THE battle lines are clearly drawn over the proposed port tunnel. On one side are its sponsors, the National Roads Authority and Dublin Corporation, supported by the Automobile Association, the Chamber of Commerce, the Dublin Transportation Office, IBEC, the road haulage sector, residents of Drumcondra and Dublin Port.
On the other side are residents of Marino and Whitehall, who fear that it would destroy their environment and even, possibly, their homes; An Taisce and the Green Party, which believe that alternatives have not been adequately examined; and several northside TDs and councillors who are worried that they might lose their seats.
The strength of public feeling on the issue, particularly in Marino and Whitehall, cannot be underestimated. People are genuinely fearful of the consequences of burrowing under some 290 homes in the Marino area, while in Whitehall local residents are concerned about noise and air pollution emanating from the tunnel portals.
Opposition to the £130 million scheme became even more intense last year following the release of a major report by Britain's Health and Safety Executive, which drew attention to at least 39 "incidents" worldwide, some involving loss of life, where tunnels were being bored using the preferred New Austrian Tunnelling Method (NATM).
Residents of Marino were also alarmed to learn - from Dr Adrian Phillips, professor of geology at Trinity College - that the southern part of their area lay in a geologically unstable "fault zone" where tunnelling would not be advisable. This assertion has been denied by the corporation and its engineering consultants.
While we accept that Dr Phillips would have a reasonable knowledge of Dublin's geology, we have no evidence that there is a significant fault zone within residential areas," said Mr Sean Mason of Geoconsult Arup. "If the rock was as highly fractured and unstable as he is suggesting, we wouldn't have to drill and blast through it."
The project design team has also denied that its geological assessment was derived from three boreholes, as claimed by Prof Ian Clayton of Surrey University, who has been engaged by the Marino Development Action Group.
"What we know is that we've done 100 boreholes and 40 trial pits," said Mr Gerry Murphy, the corporation's project engineer.
He believes that Prof Clayton's claim was based on a misunderstanding of the data.
The three boreholes referred to were drilled in 1991 when Ove Arup and Partners was engaged as consultant for the Eastern Bypass motorway scheme. Since then, two further phases of geological testing had been carried out, the latest in April 1996.
The project engineers have written twice to the action group requesting a copy of Prof Clayton's report, without success. "The MDAG will only communicate with us through their lawyers," Mr Mason said.
Mr Hugh Cregan, one of the corporation's engineers, added that the professor had been supplied with 2,400 pages of site investigation data.
However, people in Marino are mystified that the design team would choose the controversial A6 "route, tunnelling under so many homes in the area, when there was the option of running it through virtually vacant land further west; notably the grounds of High Park Convent and All Hallows, between Swords Road and Grace Park Road.
But the engineers insist that this corridor would be considerably longer and, therefore, more costly. And because more of the dual carriageway would be open cut rather than tunnelled, such a route would be less desirable environmentally.
"We're trying to find a balance between cost, environmental issues and construction disturbance," Mr Murphy said.
The engineers concede that there would be "a certain amount" of vibration in the Marino area as the proposed tunnel is blasted through limestone rock beneath people's homes. But locals simply do not believe assurances that there would be "absolutely no environmental effects in terms of noise or disturbance" after the tunnel is built.
Mr Mason attributes this scepticism to "fear of the unknown", due to the fact that Ireland does not have any road tunnels.
Oslo, on the other hand, is "criss crossed by tunnels" and six Dublin city councillors who went there last month on an information visit were apparently impressed.
"Because the Oslo tunnels early very large traffic flows, they have brought about major environmental benefits in terms of relieving the city centre, making it a much more attractive face," said Mr Murphy.
"In the centre, right in front of the city hall, a plaza that used to have 30,000 cars per day going through it is now pedestrianised."
The councillors also visited London to view work in progress on the Heathrow express rail link, where ban NATM collapse undermined an office building at the airport in 1994, and a £2 billion extension to the Jubilee underground line, which also involves using this controversial construction method.
Again, they were apparently quite impressed.
Mr Murphy stressed that the Dublin Port Tunnel engineers were "looking at all the options," as requested by the City Council last October, and they were not engaged in a "rubber stamping" exercise.
Indeed, they appear to accept that they cannot return to seek the council's approval for the A6 route without some modifications.
They also accept that the proposed location of the tunnel portals in Whitehall, some 30 metres from the nearest houses, presents a problem.
Local residents are fiercely opposed to this aspect of the scheme and have called for the portals to be relocated much further north on the M1, in the industrial zone beyond the Northern Cross interchange.
The engineers argue that this would add £42 million to the overall cost of the project.
Even though studies show that the pollution levels would be within EU and WHO standards, it is almost certain that an air filtration system will be devised to minimise emissions from the tunnel's ventilation ducts.
Noise is another major concern, with existing levels - long before the tunnel comes into operation - measured at a relatively intolerable 72 decibels. The consultants have now been asked to come up with a solution to reduce this figure to less than 68 decibels, the standard in Britain at which noise abatement measures are triggered.
This year's general election is seen as a "bedevilling factor", especially if it is held in the autumn. City councillors - many of whom are TDs seeking to retain their seats - may be reluctant to take a decision on such a controversial issue in advance of the poll, and this means that it could be delayed, even further.
But with so many "heavy guns" supporting the project, the MDAG fears that the contentious A6 route may be forced through the City Council, based on such arguments as that it is needed to deal with Dublin's growing traffic crisis, to relieve the Liffey quays of juggernauts and to capitalise on the availability of EU funding before it runs out.
Describing the scheme as "not just imperfect, but totally wrong", the action group said: "A major infrastructure project such as a port access route must be 100 per cent right in terms of viability, health and safety, value for money and soundness of construction. All concerned parties, including residents, must have a pro active involvement."
