Filming took place on actual tube tunnels, albeit disused ones.
The second stage endorsed an immersed tube tunnel as the preferred scheme versus a bridge (either fixed or opening span).
In 1992, the Minister approved a Bridge Order for a four lane immersed tube tunnel.
Temperatures underground slowly increase as the ground around the tube tunnels warms up.
Unlike surface railways, the Waterloo & City has underground tube tunnels.
In the early stages an immersed tube tunnel was considered, which was thought to be too expensive.
The Conwy Crossing, an immersed tube tunnel was built under the estuary during the late 1980s and early 1990s.
There they combined their energistic power and started to systematically smash the tube tunnels.
When completed, it will be the world's deepest undersea immersed tube tunnel.
Immersed tube tunnels, sunk into a body of water and sit on, or are buried just under, its bed.