Columbia subject headings:
Harvard subject headings:
Railroads--Austria--Vienna--History.
Subways--Austria--Vienna--History.
Traffic engineering--Austria--Vienna--History.
Vienna (Austria)--Transportation--History.
Wiener U-Bahn--History.
Princeton subject headings:
Railroads--Austria--Vienna--History.
Subways--Austria--Vienna--History.
Traffic engineering--Austria--Vienna--History.
Vienna (Austria)--Transportation--History.
Wiener U-Bahn--History.