On 10th November 1947, Sigalin started working on the W-Z route project. It was one of the most important of BOS’s projects during the first years of the reconstruction. Józef Sigalin, Zygmunt Stępiński, Jan Knothe, and Stanisław Jankowski created a modern project that also satisfied those who advocated for the rebuilding of monuments. The opening of the W-Z route coincided with beginning of socialist realism in Polish architecture. As Bolesław Bierut, a Polish communist leader, said:
Ideology in architecture is a perfect form of embodiment. What can portray our goals better than new cities.
The team that built the W-Z route was rewarded for its success with a commission to plan an architectural complex in the city centre. The project was built with the ideals of socialist realism in mind. Not only did it consist of residential areas for workers, but the project also had alleys and monumental public squares. The Marszałkowska residential area was never fully completed, but the project still became a sign of a new era. Sigalin wrote:
We are not rebuilding the city, we are creating something completely new. We are changing the Warsaw landscape. It’s time for Warsaw to have a scale suitable for a big modern city, the capital of socialist Poland.
In 1951 Józef Sigalin took over the role of chief architect of Warsaw. After Sigalin took office, Warsaw’s Old Town and New Town were both rebuilt, and he was responsible for the general concept (each building was designed by a different conservator-restorer). Sigalin perfectly understood the importance of having historical sites in the capital, even if it was contrary to his own beliefs. He was trying to rebuild Warsaw into a modern city, with thoroughfares and socialist-realist residential areas, but he knew that due to sentimental, emotional, and symbolic reasons the Old Town had to be rebuilt.