Unfortunately I didn't find any traces of the Expresso Urbano in Buenos Aires during my holidays. My great tour guide of the city had heard of the system, saying it had been installed at a time when there was much Europeanisation of the city, but that it has not been adequately maintained (or well documented), and like many other infrastructures, fell into disrepair.
While I was hunting for tubes in South America, there were exciting pneumatic happenings in my resident country, The Netherlands. In a park in Groningen, an installation of transparent pneumatic tubes, powered by a household vacuum cleaner, provided delight to passersby.
Designed as a "more accessible, less world-ending, foamier version" of pneumatic tubes, the installation of tubes, containing 1000 black sponge balls whizzing around, is a creation of the artist Niklas Roy.
The installation is interactive - park visitors can change the airflow direction and speed of the balls through motion sensors. The artist has uploaded his own tube cam footage, using a spy camera. You can watch the Fantastic Voyage here.
All images are the artists, used under the creative commons lisence. You can find many more photos of the installation here and of the making of the installation here.