An Inside Look at How Sweden Is Building the World’s Second-Longest Tunnel

The solution settled upon involves taking nothing less than 18km (11 miles-plus) of the bypass underground, with twin tunnels running three lanes abreast in each direction. Comprised of three tunnel sections in total, the winning design means that the E4 bypass avoids six nature reserves or places of cultural significance, including grounds of Drottningholm Palace—a UNESCO world heritage site on the island of Lovö—and the need for bridges over the crystal waters of the Mälaren strait. Not for nothing either, E4 will be one of the largest underground highways in the world, with its longest tunnel section spanning 16km (nearly 10 miles) from the bypass’ southernmost point.

At its deepest, the highway will bottom out at 80m (close to 90 yards) below the surface of the Mälaren.

Source: arstechnica.com