Mexico City's Anillo Periférico is an iconic outer beltway that traverses around the city. Although planning for the project began as far back as 1925, the "second floor" of the structure was constructed between 2002 and 2005. It's considered one of the most important 21st-century public infrastructure projects in Mexico City. Its pillars are also famously very grey, pragmatic, and dull. 

In 2016, architect Fernando Ortiz Monasterio, of the firm "Verde Vertical," started an online petition outlining a project to install vertical gardens on the famous concrete pillars. The project was not only designed to beautify the pillars, but also make a dent in carbon pollution. The petition was a huge success, with well over 80,000 signatures by the time it was approved by the Mexican government. 

Partially funded by private corporations (with the caveat of using much of the pillars' space for advertising), work on the gardens began by the year's end. Today, around 1,000 similar pillars supporting the second floor of the Anillo Periférico now feature Vía Verde Vertical Gardens. 

While these plants are able to absorb a significant amount of carbon and particles from the capital's polluted atmosphere, their purpose is mostly aesthetic. Ortiz Monasterio himself has admitted that 1,000 vertical gardens can only put a mere dent in the megalopolis's carbon output.