• Electric scooters, which have exploded in popularity since 2017, claim to be carbon-free. But a new study has found they emit about half as much as a conventional car.
  • The aluminum, rubber and lithium used to make these short-lived devices are the main culprits, the study found. 
  • Scooters are often recharged by many people driving cars, which also adds to their carbon impact.

In just two years since electric scooters first widely appeared in the U.S., they've displaced shared bikes as the most popular mode of transportation. About 85,000 scooters are now available in over 100 cities, while the startups that run them—the likes of Bird, Lime, Spin, Skip and Uber and Lyft—have scooped up more than $5 billion in venture capital funding.

 

A big reason for the explosion of scooters is their perceived eco-friendliness. "Cut back on CO2 emissions," proclaims an ad by scooter startup Bird. When a person finishes a ride on a Lime scooter, the app tells them, "Your ride was carbon free."

But the vehicles actually emit much more than they claim, a recent study concludes. For every mile driven, scooters emit about half as much as a typical car, concludes the study, titled "Are e-scooters polluters?" Published last week in Environmental Research Letters, it appears to be the first scientifically rigorous look at the environmental impact of these trendy devices.

"We wanted to look at the environmental impacts beyond what you'd see as a user—the aluminum that goes into the frame, the lithium-ion battery, the transport from China to the U.S., the independent contractors who are driving around in their personal vehicles at night filling them up," said Jeremiah Johnson, a professor of Environmental Engineering at North Carolina State who coauthored the study along with students Joseph Hollingsworth and Brenna Copeland.

The researchers pointed to two environmental culprits in a scooter's existence. The first is the materials. The aluminum frame, rubber tires and lithium-ion batteries that make up a scooter account for more than half of its emissions—more so because a scooter's lifespan can be shockingly short, somewhere in the range of one to three months. (The impact of transporting the scooters from China to the U.S., by contrast, is "trivial," the authors found, because the global trade network is so efficient.)

Nearly as much—about 40%—comes from the process of re-charging them. At night, when few scooters are in use, an army of gig contractors collect abandoned or badly parked rides and recharge them. These collectors are paid per scooter collected and, more often that not, use their personal cars to move the rides around. The electricity used to charge a scooter makes up just under 15% of its emissions.

Even with all that, scooters can be a greener form of transportation—if people choose to, say, scoot to the grocery store instead of driving. "The challenge is, we're not typically displacing car travel with scooters," Johnson said. A survey in Raleigh found that only one-third of scooter trips replaced driving. Most of the rest replaced trips that would have been made on foot or by bike, both of which are essentially zero-emissions forms of transport.  

This study could provide impetus for cities to crack down on scooters even further. Governments have been on the warpath against these devices, which have now been implicated in eight deaths and are accused of littering up sidewalks.

But industry defenders say the kinks—many of which are a product of a new, unregulated tool in an unfamiliar market—can be ironed out as the industry matures.

The first generation of scooters was based on models popular in China, where people often use them for trips of a mile or less to a transit stop. "It wasn't designed for the kind of use it's getting now, and it wasn't designed for these longer trips," said William Henderson, CEO of Ride Report, a software provider that helps cities track and manage scooter use.

Their flimsiness is one reason that some scooter fleets have an average lifespan of under a month, Henderson said. Now some manufacturers, such as Bird, are coming out with more durable scooters, explicitly designed to carry two riders on longer trips.

That leaves overnight charging and re-distributing scooters as the main driver of scooter emissions. The North Carolina State researchers recommend that scooter companies centrally manage that process so it's efficient and less polluting—as opposed to the favored method today which seems to leave charging in the hands of competing gig workers using private vehicles. Companies are likely to balk at this pricier option, but Ride Report's Henderson says it, too, is an eventual possibility.  

For example, Portland, Oregon, requires scooter companies in the city to report all emissions associated with their gadgets. "Now, all of a sudden, because of the very existence of that data, you're seeing competition to reduce that," he said.