Static green roofs and walls are becoming fairly common, but what about moving gardens? A company called Phyto Kenetic, created by Spanish landscape artist Marc Grañén, is now creating green roofs for buses. The green roofs keep bus temperatures cooler and can utilize air-conditioning condensate for irrigation. The plants grow in lightweight hydroponic foam, rather than in soil.

Phyto Kenetic’s prototype is currently transporting tourists near Girona, Spain, but an entire fleet could become a reality in Barcelona. As stated on the company’s website, the average useful roof space of a bus is 20 m2 (215 ft2). For cities with large bus fleets, these moving gardens could account for a significant amount of green space. According to New York City’s Metropolitan Transit Authority, the city operated 5602 buses in 2012, which could represent a green roof space of 112,000 m2 (1.2 million ft2).