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  • 08.29.13

Why Not Put Green Roofs On Buses?

A landscape artist envisions a future of public transport when all buses and vans sport greenery.

Tourists in Girona, Spain, may have noticed something strangely pastoral about the city’s public buses. Or just one in particular. The Phytokinetic Bus is painted green, has a green roof, and shuttles visitors to and from a nature reserve. More important, its creator says it’s truly sustainable transport. Very verde, and the first of its kind in the world.

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Seen from the sidewalk, the extraordinary nature of the autobus is barely visible. Only a few tall weeds indicating its existence, and it would be easy to suspect your usual thin layer of greenwashing. Then you notice the actual garden, a hearty, if scrappy, plot of shrubs and (some) flowers.


The PhotoKinetic bus is a creation of Catalan landscape artist Marc Grañén, who hopes it’s a precedent for future vehicles-turned-mobile gardens that will contribute to the health of dense cities. “Urban green areas are crucial for phyotosynthesis, vital for purifying the air we breathe,” he says.

These roof gardens in motion function as CO2 sinks. The Phytokinetic roof absorbs CO2 emitted by the bus as it makes its way across town. The plantings release oxygen that helps clean the air and mitigate environmental heating. The garden also naturally cools the interior of the bus, giving the air conditioning system a break and, as Grañén tells Co.Design, leading to “huge” energy savings. Tests revealed that the prototype roof significantly lowered temperatures inside the bus by 3.5C (38.3ºF).

“Many people are worried about the extra fuel burned for the extra weight that represents the Phytokinetic roof,” says Grañén, who explains that his prototype more than compensates for that, as the roof he’s designed is incredibly lightweight. He swapped soil out for a hydroponic foam just 2.75 inches thick. He then treated it with an impermeable spray that traps humidity but sheds water. The thin covering keeps the weight off the bus’s frame.


The garden is watered using condensation drawn from the bus’s air conditioning conduits, which are sandwiched between the ceiling and the plant bed. A stainless steel mesh anchors the foliage so there’s no risk of it spilling over the sides of the bus or onto its front windshield should the driver makes a sharp turn or hit the brakes.

Grañén emphasizes how grounded the vehicle is in the complicated legality of the city and public transport code: “It runs with all the required legal permissions and certificates and, furthermore, has passed all the security tests.”

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The system is already a patented reality, near-ready for distribution and expansion, which, of course, Grañén is busy developing, in diverse applications. He recently completed a garden roof for a van that similarly passed inspection; he will exhibit it on September 9 at the International Green Infrastructures expo in Nantes, France. He’s also working to graft his gardens onto electric buses and prototyping new watering methods. It’s a fertile plan to put in motion for our cities.

About the author

Sammy is a writer, designer, and ice cream maker based in New York. He once lived in China before being an editor at Architizer.

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