The tunnel is the major element of the project.
After serious consideration and an exhaustive environmental impact study it was agreed that a tunnel under the river Shannon offered the best long term socio-economic to Limerick and the region.
The tunnel is an immersed tube tunnel measuring 675m in length. The tube will consist of two bores, one for southbound traffic and the other for Northbound traffic. Each of the two  bores comprises a two lanes with emergency walkways on each side.
Five Tunnel Units will be cast in an area north of the Shannon. These units will be floated out and sunk into a pre-dredged channel across the river. The tunnel is completed by cut and cover sections at each end and approach ramps.