Gotthard Tunnel

SEDRUN, Switzerland--Deep under the Swiss Alps, workers are putting the finishing touches on the world's longest tunnel. This is the Gotthard Tunnel, and at 57 kilometers long and 800 meters below the surface, it is intended to drastically slash the amount of truck traffic carrying cargo over the Alps.

The project is nearly 20 years in the making and is expected to be completed in 2017. And because it is not just one tunnel, but two that are each one-way, the entire system required more than 151 kilometers of tunnel excavation, counting crossover tunnels, emergency stations, and other sections.

Seen here is the fork where trains can continue to head in the direction they were going, or switch to the crossover tunnel. That is expected to be done in cases of maintenance on one of the two one-way tunnels, or when there is an accident.