The idea of building the crossing using a floating tunnel or a seabed tunnel has been thoroughly evaluated.
Solutions involving underwater tunnels (floating) and seabed tunnels (beneath the seafloor) were extensively analyzed during the early years of the study for a stable crossing. Both scenarios were later discarded for several reasons, each of which is summarized below.

Seabed tunnels

• vulnerability to seismic activity, particularly regarding deformations or ruptures of the structure due to residual ground movements—even modest ones—resulting from direct interference with several active faults, especially in the sea. In this scenario, the vulnerability is higher than that of the floating tunnel solution. On the other hand, a bridge is insensitive to even significant ground movements, up to approximately 1 meter;
• considerable depth of the tunnels (up to 250 meters below sea level), requiring the construction of tunnel ramps with significant lengths and steep gradients. Given a Strait crossing of approximately 3.9 km, the road tunnel would need to extend 35 km, while the railway tunnel would span 50 km. These lengths are a result of limitations related to the gradients and the need to maintain seabed cover varying between 50 meters and 120 meters along the entire stretch. Consequently, for example, traveling between Reggio Calabria and Messina would require driving for approximately 70 km underground;
• longer travel times;
• difficult access for rescue or evacuation operations in case of accidents or natural disasters;
• possible unforeseen events during the works;
• exposure to sabotage.

Floating tunnels

• very high impact on the marine environment: the placement of floating pipes at shallow depths (40-50 meters) and their anchoring to the seabed at depths exceeding 200 meters would cause substantial disturbance to flora and fauna (difficult to mitigate), as well as to sea currents;
• uncertainties about structural safety and compliance with performance requirements.
• lack of previous construction in areas with high seismic activity and significant sea currents, leading to uncertainty regarding construction technologies, high risks during construction, substantial costs, and difficulties in predicting outcomes;
• maintenance uncertainties;
• impact hazards related to sinking ships;
• exposure to sabotage.