The issue of city overcrowding is a reality that many countries have faced with creative solutions, as the Chinese authorities in the mountainous city of Chongqing have demonstrated when designing the surface metro line for that metropolis whose population density reaches the 8.5 million people.
With little space to expand the monocarril line through the dense urban mesh of the city, the solution was to pass the train through a group of buildings. In effect, Line 2 of the Chongqing Rail Transit (CRT) crosses the sixth floor of an apartment block in Liziba. The building has 19 floors, with people living in them. To board, you just have to access the platform between the sixth and eighth floors.
This was the way to design a fast and simple means of transportation in that city made up of many mountainous areas, dwellings and many rivers, a set of characteristics that makes impossible the construction of a traditional underground network.