Also, an underground track consumes much more energy and is less safe.

The futuristic structure was fluid and looked like a sleek, curvilinear glacier atop the underground tracks.

The 14 underground tracks are accessible by seven stairwells, five of which are equipped with escalators.

The tracks for this system are a combination of elevated, ground-level, and underground tracks.

The construction of the underground track and station platforms also required more money then a ground-level track.

When the work of underground track started, the station was destroyed.

During those years, his music policy ranged from playing commercial to underground tracks, and much in between.

It has 18 operational stations along 27 kilometres (16 mi) of underground track.

The underground tracks opened on August 19, 2012 replacing the ground-level tracks.

The name of this underground track is Wehrhahn-Linie.