John Metcalfe was CityLab’s Bay Area bureau chief, covering climate change and the science of cities.
Attention, media: Please stop writing about bus-roof gardens as if they could actually exist in real life.
Attention, media: Please stop writing about bus-roof gardens as if they would actually work in the real world.
Yes, I know it's an irresistible idea. Take the underutilized tops of city buses and transform them into verdant patches of pastureland chugging along at 35 m.p.h. These nomadic gardens would not only look enchanting from above, the thinking goes, but would add rare green space to concrete-besotted burgs. The roofs of New York's 4,500-something buses, for instance, could support 35 acres of green life equal to four Bryant Parks.
That calculation comes courtesy of Marco Castro Cosio, an NYU interaction-designer grad who is almost single-handedly responsible for spreading the gospel of bus-roof gardens. In his 2010 thesis on the subject, Cosio laid out a buffet of supposed benefits of a chlorophyll fleet, including:
Mitigation of Urban Heat Island Effect
Acoustical and Thermal Insulation
Storm Water Reduction
Storm Water Management
Public Education and Recreation
Reclaiming Forgotten Real Estate
Sound too good to be true? It is. Nevertheless, Cosio's “Bus Roots” idea has garnered loads of praise, earning the runner-up spot in Designwala's 2010 urban-design competition and landing in 2011's Festival of Ideas for the New City, an event in NYC meant to “harness the power of the creative community to imagine the future city and explore the ideas destined to shape it.”
This is currently not happening.
Publications and websites from France, Japan, Canada, Germany and elsewhere have similarly swallowed Bus Roots uncritically, publishing Photoshopped images from Cosio's thesis that suggest these buses could be out there right now, carrying passengers. The most recent offender is Wake Up World, which ran with this Feb. 27 headline: “Gardens Flourish on Top of City Busses.” Three problems: “Gardens” should be singular, because there's only one garden, a small prototype atop the BioBus that's growing sedum. “Flourish” is much too enthusiastic a verb for what the sedum is doing; the ornamental stonecrop basically sits there at ankle height doing nothing. And just to be picky, buses is spelled wrong.
"I am very surprised" about Bus Roots' enduring popularity, Cosio said Friday afternoon by phone, noting that two European magazines had contacted him about it just this week. The designer says he's been talking to NYC officials about possibly launching such a frondy bus this summer, but has no agreement yet. “It's going slowly."
To help reality-check this bus-garden idea, and with luck lay Bus Roots gently into its grave, I went to Aaron Overman, deputy associate director for the District Department of Transportation in Washington, D.C. Overman helps run D.C.'s herd of Circulators and knows a thing or two about bus design and operation. He pointed out several potential problems with Cosio's concept, the first being...
Sure, a widespread adoption of these gardens could theoretically remove some harmful carbon dioxide from the air. But how much will their mechanical pack animals sweat out in return? By Cosio's own estimates, a garden could weigh as much as 2,000 pounds. The vehicle is going to have to burn a lot more gas to compensate for this extra burden. Buses are not the friendliest gas-burners to begin with, eating 3 to 4 gallons of fuel per mile, and slapping a load of dirt, soil and plant matter to its roof will make them into exhaust-spewing Sherman Tanks. “This would be a permanent load on the bus itself and you'll burn more fuel just moving that additional weight through the street,” Overman says. “It just doesn't make sense from a global-output standpoint.”
“There would need to be some sort of irrigation equipment and water on the bus – again, more weight and fuel consumption,” says Overman. Granted, plants like sedum don't require frequent watering to survive, normally. But this is not a normal garden. The soil layer is much thinner than what you get in a backyard. Buses often run on marathon schedules from 5 a.m. to 1 a.m. on weekdays, exposing the plantings to long periods of direct sunlight and dehydrating currents of wind created by the movement of the vehicle. It would take a special kind of plant to withstand such an alien environment – Spanish moss stapled to the roof might work. Otherwise, somebody would need to water the beds regularly to prevent plant death.
Add water and you create the potential for leaking. Bus roofs would require “additional layers to ensure that water does not drip through to the passenger areas,” Overman says. Even buses with well-waterproofed hides might have seals between joints that could deteriorate enough to turn the inside of the coach into an indoors rainforest.
This is more realistic: the Bus Roots prototype garden atop the BioBus. (Image via Bus Roots)
In Cosio's prototype, the plants embed their roots in a textile commonly used in the green-roofing industry. The beds rest in a Tyvek membrane and are surrounded by an aluminum frame. I would still think that should the bus driver hit the gas pedal while chugging up a hill, he would lose a rear chunk of the garden to spontaneous erosion. Likewise, if he were to brake hard in traffic, the car ahead of the bus could become covered in soil and plantings.
Buses are required to have multiple evacuation points in case of a serious accident. Often these exits are located on the ceiling, forming impromptu doorways when a bus is knocked on its side. Regulators would not look kindly on any emergency scheme that requires people to claw through dirt and leafs to reach safety.
Although the roofs of city buses look barren, they're not. Take D.C.'s fleet. There are six or seven different devices on the roof that keep the bus functioning properly: GPS equipment that makes predictions of arrival times; radio antenna to maintain the driver's link with a supervisor; a wireless connection for the fareboxes to keep track of the day's revenue and passenger count. Bus designers would have to be mighty creative to make room for both a garden and all this gear. Antenna trees, perhaps?