Bangkok's elevated railway, the Bangkok Transit System (BTS), is fully operational since 1999. This two-line concrete shuttle snakes around the buildings, 20 meters above our heads, and serves mainly rich neighbourhoods downtown.

The geology of the Bangkok area is characterized in such a way that it is almost impossible to build underground : the city, built on swampland, is crisscrossed by khlongs, canals that drain the humidity of the ground. It is therefore not surprising to see that all happens high above our heads. Indeed, the buildings' first floors - and sometimes up to the tenth floor - are often reserved for car parks and the new metro line is built several feet above the ground.

Besides, traffic conditions have somewhat improved since the launch of the Skytrain. Would one way to keep away from pollution and traffic noise be to manage the new flows a few feet above the ground, just like many urban science fiction writers have described ?

Traffic conditions may have improved, but the Skytrain fares are still prohibitively expensive, meaning that they are only affordable for an elite. In city planning, just like in graphic arts, a clear line can divide, separate or bring together two territories, two populations. Here, people from “above”, who can afford the metro, never touch the ground; footbridges and air-conditioned hubs are connected directly to office towers and shopping centres, well above pollution and the suffocating heat of the jammed avenues down below. A Skytrain passenger is supposed to travel six times faster than bus or tram passengers, who in return travel six times cheaper. This is very symbolic of a two-tier society !

Is this wild vertical city planning therefore associated with a form of social segregation and “stratification” ?