ROCK SOLID SAFETY

The Budapest Metro is Europe’s second oldest subway – only the London Underground is older. For a fourth line added in 2009, a 7.4-kilometer tunnel was dug under the Danube. It joins the districts Buda and Pest. Two new platform tunnels under the Danube were also created. Before the drilling started, the soil in the upper part of the tunnel was frozen with cryogenic liquid nitrogen. The resulting stability made the underground construction site safer. Freezing the soil also prevented water penetration. By the time the project was completed in April 2010, a total of two million cubic meters of nitrogen had been used.