It carries two lanes of European Route E16, and was the final link completing the main highway that now enables car travel between Oslo and Bergen with no ferry connections and no difficult mountain crossings during winter.

[3][4] Beginning in 2025 and for around four years, the tunnel will be completely closed for fourteen hours each night for upgrades to meet recent changes to EU safety regulations.

The tunnel begins just east of Aurlandsvangen in Aurland, goes under a mountain range, and ends 5.5 kilometres (3.4 mi) south of Lærdalsøyri in Lærdal.

Its design takes into consideration the mental strain of driving through a long tunnel; it is divided into four sections, separated by three large mountain caves (with parking areas available) at 6-kilometre (3.7 mi) intervals.

Emergency phones marked "SOS" are installed every 250 metres (820 ft) for contacting police, fire departments, and hospitals.

The Lærdal Tunnel is the first in the world to be equipped with an air treatment plant, located in a 100-metre (330 ft)-wide cavern about 9.5 kilometres (5.9 mi) northwest of Aurlandsvangen.