"It's an oxymoronic situation," Sean O'Neill of the National Roads Authority said. "The interest people have in the construction of the tunnel is showing the need for the tunnel."

Over 7,000 people attended Saturday's Open Day - 5,000 more than expected - to examine one of the biggest construction projects undertaken in the West of Ireland.

Six coaches and three mini buses circled the construction site from 10am to 5pm bringing members of the public on the 10 minute tour.

Over 100 NRA, DirectRoute and Strabag staff volunteered for the day, directing traffic, supervising car parks and answering questions about the project.

The five tunnel elements are currently being fitted out for the next major phase of the tunnel construction, immersion in a pre-dredged channel in the river on August 7.

Each tunnel element is approximately the length of a football pitch, 100m; as high as a two storey house, 8.5m; wide enough for two lanes of traffic in each direction, 25m; and weighs in at 20,000 tonnes giving a combined weight of a staggering 100,000 tonnes.

DirectRoute also provided an information centre with a scale model of the scheme for visitors who took part in the tour.