SEAN WYNNE,
Sir, - Can I clear up, once and for all, that at 4.9 metres clearance height, with an operating height restriction of 4.65 metres, the Dublin Port Tunnel is higher than the highest European tunnels where height limits apply.
In Italy the limits are 4.75m; the Dublin Port Tunnel is 150mm higher.
Other limits are:Austria, 4.7m (4.5m for city tunnels); Switzerland, 4.7m; Norway, 4.6m; Germany, 4.5m; France, 4.3m to 4.75m. Individual tunnel operators then impose their own, lower, height restrictions for operational or safety reasons. At 4.65m operational height, the Dublin Port Tunnel is higher or on a par with all of them. It will be able to take 9,000 trucks off the streets of Dublin every day, along with 2,500 cars, with substantial benefits in reducing heavy goods vehicle traffic through Dublin city centre. It will also accommodate double-deck buses (4.57m.
The Dublin Port Tunnel complies fully with the EU Directive requiring heavy goods vehicles, not exceeding 4.0m in height and undertaking international journeys, to be accommodated. Virtually all trucks using Dublin Port will be able to use the Dublin Port Tunnel, except for some very large car transporters and extra-large container vehicles, which require 5m clearance.
Unlike Europe, where tunnels can be up to 20km long, the UK does not have any tunnels as long as the Dublin Port Tunnel's 6.5km, with 4.5km underground. The UK considers its shorter tunnels to be the same as over-bridges on open roads and has a clearance height of 5.03m.
If, like the Dublin Port Tunnel, they were to allow a 250mm safety clearance for vehicles with flapping tarpaulins, loose ropes or high vehicles carrying compressible loads, the UK limit would be reduced to 4.78m. Urban UK tunnels similar to the Dublin Port Tunnel design include London's 1.4km Rotherhithe, with a limit of 4.72m, and Heathrow Airport's 0.6km tunnel with a limit of 4.6m. The 1.09km-long Conway Tunnel at Holyhead has a clearance limit of 5.1m.
Huge trucks requiring clearance of up to 5.5m, as suggested by Mr J. Kiersey, of the Transport Umbrella Group (January 23rd,) could not even be accommodated on most of Ireland's surface roads, including our new motorways, since this vastly exceeds the height at which road bridges, both in Ireland and internationally, are being developed.
Finally, the Dublin Port Tunnel is costing €450 million and is being built to the highest international specifications. We are using the biggest tunnel-boring machines in the world, capable of boring the two-lane tunnels we require. The first tunnel-boring machine will be arriving on site next month and we plan to open the Dublin Port Tunnel in less than three years' time. - Yours, etc.,
SEAN WYNNE,
Project Engineer,
Dublin Port Tunnel,
Dublin Corporation,
Dublin 2.