Just over 40 years ago, the Labour government was given a preliminary survey and report entitled Link Road Between Malta And Gozo, igniting a debate that remains open to this day.

The study, completed in March 1972, had been done by the Japanese government’s Overseas Technical Cooperation Agency.

The survey team was headed by Yoshimaro Matsuzaki, from the Honshu-Shikoku Bridge Authority.

And it included Yasuhiro Kimura, from the Tokyo Expressway Public Corporation, Hirohiko Tada, also of the Honshu-Shikoku Bridge Authority, and Ono Shigenori and Keiichi Komada, both from the Road Bureau of the Ministry of Construction.

Their task was to examine the technical feasibility of the link road construction, study the methods for constructing the link across the Gozo channel and estimate how much this would cost.

Three structural types were considered: a bridge, a tunnel and a causeway. The experts looked into two cases of building a bridge, one costing an estimated $17 million (the equivalent of $91.5 million today) and the other $14.8 million ($79.6 million in today’s money).

Both a submerged tunnel and a causeway would have each cost $17.5 million ($94.2 million today) to build.

So the experts concluded that a bridge was the most economical in terms of cost of construction.

They found that the south Comino channel – between Malta and Comino – was about 1.8 kilometres wide. The channel to the north, that is between Comino and Gozo, had a width of about one kilometre.

They believed that an underwater tunnel could have worked too, judging by the topography in the south Comino channel as noted through a rough field survey and the data acquired from a hydrographic chart.

Certain information was not available to the Japanese experts and so their plan was prepared on the assumption that the geology and tidal current of the channel constitutes the conditions favourable to the construction of such a tunnel.

However, a tunnel had been ruled out for the north Comino channel because, as their report put it, “a satisfactory profile to meet the structural standards cannot be secured by reason of the construction cost”.

The survey illustrated a common general cross section of a sunken tunnel, which was a common pattern in those days.

In that form, a provision was made for transverse ventilation to deal with the traffic volume exceeding 5,000 vehicles a day but the experts felt that jet fans would have been sufficient until such traffic volume was reached.

The costs for installing and maintaining such ventilating device were thought to have been “almost negligible”. A depth of 10 metres would be enough to secure a satisfactory sea route through the south Comino channel, the report had found.

Taking the longitudinal slope of road surface into consideration, a route width of 150 metres could be secured at a depth of 10 metres.

The experts had noted that the maximum depth in the south channel was about 24 metres, whereas the north channel was about 20 metres deep.

The survey had listed three plans in relation to the construction of the submerged tunnel.

Plan 1 was considered to be the most reliable even if it would have meant a higher cost of construction.

Presuming there was no deposit on the seabed, the bedrock would have been excavated to the depth of one third the height of the sunken tube (about four metres), which is placed in the excavated trench.

Assuming the seabed to be bedrock, in order to minimise excavation, in plan 2, it would have needed to be levelled by removing protrusions to the minimum extent and the sunken tube then installed on the levelled seabed.

In order to obtain the stability of the tube in the lateral direction, rock or debris of good quality would have been required to be placed against both sides of the tube in sufficient width.

In plan 3, the excavation on the bedrock would have applied only to limited parts and embankments would have been constructed on the sea bottom for most of the base course on which the sunken tube would be installed.

This would have required a sufficient examination with regard to the stabilisation of the embankments on the sea bottom to ensure adequate settlement of the sunken tube.

The experts also explained how the tube would be delivered irrespective of the plan chosen.

The steel shell, with a diameter of 10.3 metres and 100 metres long, would have been manufactured at a drydock, floated and towed to the site.

Concrete would then be used to form the section, keeping the steel shell afloat, which is then sunk and installed on the base course prepared on the seabed by screeding.

Rubber gaskets would have been used for the joints and each element would be connected tight by hydrostatic pressure acting on the element.

Among the three links – a bridge, a causeway and a tunnel – the most expensive to build, would have been the tunnel.

Also, the joints system to link the tunnel units together would have increased the maintenance expenses.

Number of cars, traffic volume between Malta & Gozo & total tourist arrivals (where available)

South Comino channel submerged tunnel

Lenth: About 1,400 metres
Steel material: 5,600 tons
Reinforcements: 6,000 tons
Concrete: 75,000 square metres
Cost of construction: $17.5 million