For the first time, the Stadtbahn project was made concrete in 1890, when Krauss & Co. submitted drafts as a basis for the official negotiations, although they have undergone numerous changes during the following years. The reason for the renewed approach to Stadtbahn construction was on the one hand the continuing economic upturn in Austria, and on the other hand a major expansion of the city of Vienna, adding districts 11 to 19 were added to the existing districts 1 to 10. As a result, the city increased from 55 to 179 square kilometers and the population increased from 800,000 to 1,300,000, causing the Stadtbahn project to gain in urgency. At the same time, the western expansion of the city required the expansion of the Stadtbahn project to take into account the newly incorporated municipalities from the beginning. So the planners added the so-called suburb line to the project, even though the namesake suburbs now also all belonged directly to the city.