Complex sentence: A second rail tunnel through the pass, the Gotthard Base Tunnel, was opened on June 1,2016, as the longest tunnel in the world, reducing travel time between Zürich and Lugano to 1 hour 40 minutes.
Split into simpler sentences: A second rail tunnel through the pass, the Gotthard Base Tunnel, was opened on June 1,2016. The new tunnel is the longest tunnel in the world, reducing travel time between Zürich and Lugano to 1 hour 40 minutes.