With a recent vehicle survey showing that the €625 million Dublin Port Tunnel will be too low for 4.5 per cent of trucks - rising to 10 per cent in 2013 - the haulage sector has intensified pressure to raise its height, writes James Nix.
Mr Austin Gilligan, general manager of Gwynedd Shipping, says the tunnel should have the same clearance as a dual-carriageway: "Hauling paper tissue once accounted for 100 journeys a month: now, with high-clearance trucks, we carry the same volume in 56 trips."
The standard height for dual carriageway in Ireland, set by the National Roads Authority, is 5.3 metres. This gives an operational clearance of 5.05 metres, allowance of 25cm being made for tarpaulins, ropes etc. Even though the Dublin Port Tunnel is dual carriageway, plans for the €625 million project envisage an operational height of 4.65 metres.
Six years ago EU-funded research found that the use of bigger grocery lorries would reduce total vehicle movements in that sector by 15 per cent. The number of heavy goods vehicles in Britain has dropped from a peak of 593,000 in 1967 to 422,000 in 2001. Promoting high-clearance vehicles has been official policy at Britain's Department of Transport since 1998.
In Ireland successive reports by the Environmental Protection Agency (EPA) identify spiralling road transport emissions as the greatest threat to our air quality. With the coming into effect of the Kyoto Protocol on Climate Change, a failure to stay within our emission targets will result in penalties from 2008.
Under Kyoto, Ireland agreed to cap emissions of carbon dioxide and other greenhouses gases at 13 per cent above their 1990 levels. Regrettably, our rate of increase is already in the region of 25 per cent.
Before being replaced with a 5.3-metre structure, the East Wall Road had a bridge 4.6 metres high. It was the most struck bridge in Ireland - 104 impacts from 1985 to 2002, 53 of them after 1998.
Originally, the Transport Umbrella Group sought to have the Port Tunnel brought to standard dual carriageway height. However, in a meeting with city officials last December, the group agreed that an operational height of 4.9 metres would be satisfactory. This would give an operational clearance 15cm below standard but 25cm more than the original blueprint.
A review of the feasibility and cost of adjusting finished road levels and overhead equipment fittings in the tunnel shows a 4.9-metre operational clearance can be achieved at a cost of betwee €20-30 million, according to Tim Brick, deputy city engineer.
(James Nix is pursuing a masters in the design of transport networks at the DIT)