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Size matters

Tunnelling - Dublin Port Tunnel

Is Dublin Port Tunnel being built too small? This debate has been raging for three years, yet the problem first emerged when regulations limiting the height of heavy goods vehicles in Ireland to 4.25m lapsed in the early 1990s.

The tunnel is designed for the European standard clearance of 4.65m. This is too low for the new generation of super trucks which are becoming more common in Britain where the motorway clearance height for vehicles is generally 5m. Although less than 2% of HGVs using the port are oversize, Britain is Ireland's biggest trading partner and the numbers are likely to grow.

But the design specification was not changed. Now, incredibly, with one year to go until the scheduled completion date, the Irish government has still to make up its mind on whether it wants the tunnel's operating cross section to be bigger.

Physically the tunnel cannot be made bigger, but the operating envelope can be increased a little by lowering the road surface and altering the ventilation system.

The issue is the cost. An estimate of $32M drawn up by consultant Atkins for Ireland's ministry of transport in November last year had to be revised after DCC challenged the dimensions used.

NMI is now in the process of producing a revised estimate, which was to be sent to transport officials last month. But one thing is certain, it would have cost a lot less if the government had decided three years ago.

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