A new study from North Carolina State University finds that while shared e-scooters may be greener than most cars, they can be less green than several other options, including, in some cases, buses. Their open-access paper is published in the journal E.nvironmental Research Letters

Using life cycle assessment, the researchers quantified the total environmental impacts of shared e-scooters associated with global warming; acidification; eutrophication; and respiratory impacts. The performance results were similar for all four types of pollution.

Life cycle environmental impacts for shared electric scooters under Base Case and alternative collection scenarios for (a) global warming, (b) respiratory effects, (c) acidification, and (d) eutrophication. Error bars represent 95% of the Monte Carlo simulations. Chan et al.

They looked at emissions associated with four aspects of each scooter’s life cycle: the production of the materials and components that go into each scooter; the manufacturing process; shipping the scooter from the manufacturer to its city of use; and collecting, charging and redistributing the scooters.

They found that environmental burdens associated with charging the e-scooter are small relative to the materials and manufacturing burdens of the e-scooters and the impacts associated with transporting the scooters to overnight charging stations.

The results of a Monte Carlo analysis show an average value of life cycle global warming impacts of 202 g CO₂-eq/passenger-mile, driven by materials and manufacturing (50%), followed by daily collection for charging (43% of impact).

E-scooter companies tout themselves as having little or no carbon footprint, which is a bold statement. We wanted to look broadly at the environmental impacts of shared e-scooters—and how that compares to other local transportation options.

—Jeremiah Johnson, corresponding author of the study and an associate professor of civil, construction and environmental engineering at NC State

The researchers also conducted a small-scale survey of e-scooter riders to see what modes of transportation they would have used if they hadn’t used an e-scooter. The researchers found that 49% of riders would have biked or walked; 34% would have used a car; 11% would have taken a bus; and 7% wouldn’t have taken the trip at all. These results were similar to those of a larger survey done by the city of Portland, Oregon.

A lot of what we found is pretty complicated, but a few things were clear. Biking—even with an electric bike—is almost always more environmentally friendly than using a shared e-scooter. The sole possible exception is for people who use pay-to-ride bike-share programs. Those companies use cars and trucks to redistribute the bicycles in their service area, which can sometimes make them less environmentally friendly than using an e-scooter.

—Jeremiah Johnson

By the same token, the study found that driving a car is almost always less environmentally friendly than using an e-scooter. However, taking the bus on a route with high ridership is usually more environmentally friendly than an e-scooter.

We found that the environmental impact from the electricity used to charge the e-scooters is fairly small—about 5% of its overall impact. The real impact comes largely from two areas: using other vehicles to collect and redistribute the scooters; and emissions related to producing the materials and components that go into each scooter.

—Jeremiah Johnson

That means that there are two major factors that contribute to each scooter’s environmental footprint. First is that the less driving that is done to collect and redistribute the scooters, the smaller the impact. The second factor is the scooters’ lifetime: the longer the scooter is in service, the more time it has to offset the impact caused by making all of its constituent parts.

There are a lot of factors to consider, but e-scooters are environmentally friendly compared to some modes of transport. And there are things that companies and local governments can do to further reduce their impacts. For example, allowing—or encouraging—companies to collect scooters only when they hit a battery depletion threshold would reduce a scooter’s impact, because you wouldn’t be collecting scooters that don’t need re-charging.

—Jeremiah Johnson

The work was supported, in part, by the North Carolina State University Department of Civil, Construction, and Environmental Engineering Research Experience for Undergraduates Program.

Resources

• Joseph Hollingsworth, Brenna Copeland and Jeremiah X. Johnson (2019) “Are E-Scooters Polluters? The Environmental Impacts of Shared Dockless Electric Scooters” Environmental Research Letters doi: 10.1088/1748-9326/ab2da8