The idea of a crossing of the River Lee downstream of the city centre came from civil engineers employed by Cork Local Authorities and the central government's Department of the Environment in the late 1970s.

Cork's suburbs were expanding and traffic was rising as car ownership increased, but the city centre's street plan, laid out in the late Middle Ages, was ill-equipped to cope.

The engineers reasoned that the congestion in the city centre and its radial routes was quickly reaching intolerable levels.

No road development in Ireland prior to that date had required such a large investment,[5] and therefore the plan met with some opposition on the grounds of cost.

In 1980, Cork Corporation commissioned DeLeuw Chadwick O’hEocha, engineering consultants, to undertake a feasibility study of options for a major highway crossing of the River Lee downstream from the city centre.

[4] The first stage of the report established that the crossing should be located in Dunkettle, rather than at Tivoli, closer to the city centre.

The second stage endorsed an immersed tube tunnel as the preferred scheme versus a bridge (either fixed or opening span).

Shipping volumes into Cork's port area was rising steadily in the 1980s, which meant that an opening span bridge was becoming less attractive every year.

A sworn Public Inquiry into Cork Corporation's application for a "bridge order" providing for a two-lane tunnel was held in October 1985.

The formal reason for this was that the minister "decided that the question of the timing of the crossing should be considered in the broader context of the preparation by the Department of proposals for the medium to long term development of national roads.

Fitzgerald, Cork City Engineer, formed an informal Technical Steering Committee for the Tunnel Project.

The IR£70 million design and construct contract was awarded by the Cork Corporation on behalf of the National Roads Authority.

Tunnel sections are constructed in the dry, for example in a casting basin, a fabrication yard, on a ship-lift platform or in a factory unit.

The scope of works consisted of dredging the main tunnel trench and subsequently backfilling the completed construction with sand and gravel.

Two barges were used to transport the dredged material 19 km (12 mi) downriver and from there to a disposal site four miles offshore.

A second cutter dredger, "Vlaanderen XV", was deployed to breach the casting basin perimeter, or "bund".

A rock layer was encountered on part of the trench line, which was dealt with by the jack-up platform "Zeebouwer".

This system proved extremely effective in removing very thin layers of recently deposited material immediately prior to immersion of the tunnel elements.

These were constructed in a casting basin located partially on the line of the tunnel south of the river at Mahon.

The outer walls and roof were cast together in a single operation, in six nominal 20-metre lengths, using special travelling formwork.

The boat unit and all the tunnel section elements were cast using grade 40N concrete with a percentage of ggbfs cement replacement, reinforcement being high strength and 16 to 40 mm diameter.

The road surface was laid in 1998/1999 and the tunnel opened for traffic on 21 May 1999,[12] roughly 20 years after the first formal studies had been prepared.