The Dublin Port Tunnel's overall cost has risen to €625 million, or €139 million per kilometre, making it by far the most expensive major road project yet carried out in the State.
The 4.5-km twin tunnel, designed primarily to cater for port-related heavy goods traffic, will function as a dual-carriageway between the M1 at Coolock Lane and a toll plaza adjoining East Wall Road.
However, it now appears to be too late to change its dimensions to cater for taller trucks, as proposed by some hauliers, because the first five sections of "cut-and-cover" tunnel at the Fairview end have already been cast in concrete.
The construction cost of the overall project is fixed at €450 million, with "early 2005" given as a completion date. However land acquisition, compensation and supervision of the contract will add a further €175 million to the final bill.
The €625 million total contrasts with the estimate of £130 million (€165 million) given in 1996 when the project was approved by Dublin City Council; it is even higher than some of its more vocal critics forecast at the time.
The cost is now being met entirely by the Exchequer, with no funding from the EU. It is also conditional on reasonable sums being awarded in compensation to householders under whose homes it is being bored through Marino.
Settlements have been agreed with almost half of those affected, ranging from €317 to €6,500, based on the location of individual properties, but outstanding claims will hinge on a crucial arbitration case at the end of this month.
Altering the tunnel clearance height from 4.65 metres to 5.3 metres to accommodate taller trucks and car transporters would cost an additional €100 million or more and could only be done by dropping its floor to the required depth.
Fifty-eight per cent of the tunnel is being bored by two Japanese tunnel boring machines, each costing €25 million. Each bore has a diameter of 11.7 metres (almost 39 ft), so in theory it should be possible to provide sufficient clearance.
However, Mr Tim Brick, the deputy city engineer in charge of the project, pointed out that the installation of structural rings within each tunnel together with fire lining, ventilation fans and variable message signs considerably reduced the clearance available.
"If we were to accommodate trucks with a height of 5.3 metres, it would involve dropping the floor by 700-750 mm. This would mean narrower lane widths which would inevitably reduce safety margins in the tunnel's enclosed environment," he said.
Other alternatives, also regarded as unacceptable, would include raising the kerb on either side to a height which would make it unusable or reducing its width to such an extent that the emergency escape doors would "stick out into the carriageway".
Apart from technical design issues, Mr Brick said that neither the National Roads Authority nor taxpayers "would thank us for whacking on the extra cost". In any case, "nobody heard of 5.3 metre trucks when this project was designed".
He said the NRA's 5.3-metre standard clearance height for motorway over-bridges was intended to allow for the resurfacing of the road underneath. "The economics of doing so in a tunnel would raise huge contractual and financial issues," he warned.
Mr Brick said a three-month survey of port-related traffic around the north port had shown that only 1.3 per cent of the trucks would not fit into the tunnel. A similar survey of the south port terminal will be carried out shortly.
Asked about a British government policy favouring 5.3-metre "high-cube" trucks for lightweight bulky freight, on the basis that this would reduce truck movements, he said they would "find themselves confined to the UK market".
Such trucks would be "out of kilter" with the 4-metre maximum vehicle height in most European countries, though Mr Brick conceded that a new port tunnel in Hamburg was being built to a height of 5.1 metres, mainly to cater for NATO tank transporters.
Ireland has no maximum vehicle heights. Legislation in 1996 limiting truck heights to 4.25 metres and double-deck buses to 4.57 metres had to be rescinded in 2000 because it had not gone through formal EU consultation procedures.
