Bird boasts that its dockless electric scooters allow customers to “cruise past traffic and cut back on CO2 emissions—one ride at a time.”
Its rival Lime claims the vehicles “reduce dependence on personal automobiles for short distance transportation and leave future generations with a cleaner, healthier planet.”
But the mere fact that battery-powered scooters don’t belch pollution out of a tailpipe doesn’t mean they’re “emissions free,” or as “eco-friendly” as some have assumed. The actual climate impact of the vehicles depends heavily on how they’re made, what they’re replacing, and how long they last.
Researchers at North Carolina State University decided to conduct a “life-cycle assessment” that tallied up the emissions from making, shipping, charging, collecting, and disposing of scooters after one of them noticed that a Lime receipt stated, “Your ride was carbon free.”
The study concludes that dockless scooters generally produce more greenhouse-gas emissions per passenger mile than a standard diesel bus with high ridership, an electric moped, an electric bicycle, a bicycle—or, of course, a walk.
The paper found that scooters do produce about half the emissions of a standard automobile, at around 200 grams of carbon dioxide per mile compared with nearly 415. But, crucially, the researchers found in a survey of e-scooter riders in Raleigh, North Carolina, that only 34% would have otherwise used a personal car or ride-sharing service. Nearly half would have biked or walked, 11% would have taken the bus, and 7% would have simply skipped the trip.
The bottom line: roughly two-thirds of the time, scooter rides generate more greenhouse-gas emissions than the alternative. And those increased emissions were greater than the gains from the car rides not taken, says Jeremiah Johnson, an engineering professor and one of the authors of the paper.
The electricity used to charge the vehicles is one of the smallest contributors to the product’s emissions. Fully half come from the raw materials and manufacturing process, which the researchers estimated, in part, by disassembling a Chinese-made Xiaomi M365 scooter, a model that Lime and Bird are known to use.
The team weighed each part, including the aluminum frame, steel parts, lithium-ion battery, and electric motor. They then relied upon the findings of earlier peer-reviewed studies to assess the environmental impacts of extracting, producing, and delivering those raw materials.
But how much these emissions add up to on a per-mile basis depends heavily on how long scooters actually last. An increasingly evident problem is that the vehicles’ theoretical operating life of around two years scarcely resembles their “nasty, brutish and often short” existence in the real world.
Scooters are variously flung into water bodies, tossed from buildings, set on fire, run over, and used in stunts. Cleanup crews in Oakland, California, fished 60 scooters out of Lake Merritt in a single month last year, Slate reported.
An analysis of open data from Bird’s inaugural fleet in Louisville, Kentucky, conducted by Quartz last year, found that the average scooter lasted just 28.8 days. Likewise, Bird itself acknowledged in investor documents at an earlier point that its vehicles last only about a month or two, The Information reported.
The other major share of emissions, 43%, comes from the additional fleet of vehicles needed to navigate around a city like Raleigh each day, collecting scooters strewn across yards and sidewalks, taking them to a central charging location, and returning them to spots where riders can find them.
Lime has made an effort to address some of the concerns raised about its environmental footprint. Late last year, the company announced it would offset all the emissions from charging its scooters and the vehicles used to pick them up by purchasing clean electricity, and investing in renewable energy and carbon offsets projects.
"We welcome research into the environmental benefits of new mobility options, however this study is largely based on assumptions and incomplete data that produces high variability in the results," Lime said in a statement. "We believe micromobility will reduce pollution and mitigate climate change through clean and efficient modes of transportation and we’re making rapid advances in technology and operations that are helping us become a more sustainable company."
The North Carolina findings are, however, consistent with some earlier efforts to evaluate life-cycle emissions or usage patterns.
The Portland Bureau of Transportation found that only 34% of the city’s riders took an e-scooter instead of driving their own car, or using a ride-sharing service or taxi. In fact, Lime itself found that about “1 out of every 3 trips” replaces a car ride, in surveys across 26 cities.
On the other hand, an unpublished analysis for clients by the Rhodium Group put the emissions figure far lower, at 28 grams per mile, the Financial Times reported. Hannah Pitt, an analyst with the research firm, said the new study’s methodology looked reasonable, but that there were some key differences in assumptions that added up to a wide gap in the end results.
Among them, Rhodium didn’t assume every scooter is picked up each night. Raleigh policy requires this, but that doesn’t mean it’s the common practice. The firm also assumed the vehicles last on the roads through their standard battery life, which Pitt says might have been too generous, given the level of vandalism and real-world wear and tear that’s since become clear.
Still, she says: “It would be shocking if a scooter’s per-mile emissions is half those of a passenger vehicle.”
The good news, according to the North Carolina study, is there are ways to reduce the emissions, including using electric or at least more fuel-efficient vehicles to collect the scooters, reducing the distance between pick-up and drop-off points, and only gathering vehicles with a low battery charge. Increasing the proportion of recycled materials, especially the aluminum, would also help.
The change that might matter most is extending the lives of scooters. If the vehicles lasted for two years instead of a few months, the study found, it would cut average emissions by about 30% per mile—and make scooters the cleaner option as much as 96% of the time.
But no surprise: walking is still going to be your greenest bet for getting around.