During the early twenty-first century, the Austrian government authorised the four-tracking of the Westbahn, which was the nation's most important rail corridor. Accordingly, the section between Vienna and St. Pölten saw the construction of two new tracks on an alignment free from challenging gradients and suitable for high speed operations, which deviated far to the North of the original line. It was along this new route that the Wienerwald Tunnel, which is the single biggest engineering structure, was constructed to convey the line across the Wienerwald mountain range. Its construction facilitate the movement of trains traversing the Westbahn to call at Wien Hauptbahnhof, the recently completed central station serving Vienna.