But the 9.8 billion Swiss franc (7.0 billion euro) tunnel is also the fruit of a popular wave of concern about pollution in the Alps with booming road traffic transiting from neighboring countries.
After 15 years of construction work, the 9.5-meter (31-foot) wide drilling machine will bore through the remaining 1.5 meters of rock to join two ends of the tunnel some 2,000 meters under a mountain.
The stage-managed event, attended by 200 dignitaries 30 kilometers along the tunnel, will be broadcast live on Swiss television and watched by European Union transport ministers at a meeting in Luxembourg.
But the spotlight will also fall on some 2,500 tunnel workers, many of whom will be feasted at a celebration just above the breakthrough point in the mountain village of Sedrun.
Eight have died since construction of the new tunnel began 15 years ago, blasting and boring through 13 million cubic meters of rock in hot and humid conditions.
The Gotthard tunnel will exceed the 53.8-kilometer Seikan rail tunnel linking the Japanese islands of Honshu and Hokkaido and the world's longest road tunnel, the 24.5-kilometer Laerdal in Norway.