An estimated 40,000 people walked under the River Shannon through the new Limerick Tunnel which opened to the public for an open day today.

It was the last chance for the public to walk the tunnel before it officially opens at the end of July.

The Limerick Tunnel took four years to construct at a capital cost of €660m, and is one of the biggest infrastructural projects ever in the Mid-West region - rivalled only by the construction of the hydroelectric power station at Ardnacrusha during the early 1930s.

It is due to open at the end of July, well ahead of its scheduled opening date of 17 September.

The tunnel will provide a fourth crossing of the river Shannon in Limerick, and will take an estimated 27,000 cars out of the city centre.

The tunnel will improve access times for commuters to the city, as well as access to Shannon Airport, Galway, Cork, Kerry and Dublin.

The open day was from 10am to 7pm, but thousands of people had already gathered from 9am to be among the first group through the tunnel.

Direct Route, the company which built the tunnel, also provided food and canteen facilities at the end of the tunnel, and park and ride facilities to help in traffic management.

They were hoping to raise over €100,000 for charities through the sale of a special commemorative brochure.