August 15, 2019

Since the recent introduction of scooters, some cities have piloted or allowed them on all streets as a potential means to reduce vehicle miles traveled. But similar to their ride-hailing peers, it has been difficult for cities to assess whether these devices are, in fact, replacing vehicle trips or siphoning away walkers and cyclists. A reduction in vehicle trips is generally tied to decreases in greenhouse gas (GHG) emissions, but recent analyses have started to question that assumption.

An article published on August 2 in Environmental Research Letters by a group from North Carolina State University assessed the global warming effects of shared electric scooters against various other forms of transportation. The authors use a life cycle analysis to assess how the material processing, manufacturing, shipping, charging, and collection of shared e-scooters contributes to greenhouse gas emissions and how they compared to the modes they are likely to replace. Their results paint a bleak picture with a 65 percent likelihood that the scooter will have more global warming impact than the mode it replaces. This includes a 1.7 percent likelihood that it could be worse than using a personal automobile. How could a small scooter possibly have a higher life cycle impact than an automobile? The short answer; scooter distribution is currently – for the most part – reliant on motor vehicles.

If you factor the scooter by itself and ignore the emissions related to the extra automobile trips needed for their collection and distribution, they are fairly benign compared to the impact of automobiles and are relatively on par with bicycles and e-bikes. From the authors’ estimate, depending on the amount of virgin or recycled aluminum used to make the scooter, the manufacturing process can contribute anywhere from 17.7 kg of CO_2-e (48% recycled materials) to 200 kg of CO_2-e (100% virgin materials). The shipping process contributes a minimal 9.54 – 3.44 kg CO_2-e depending on distance and method.

Charging the scooter itself is minimal, with a small 0.335 kWh battery giving approximately 18 miles of range. (For reference 0.335 kWh is approximately the energy that would be used to run a refrigerator for 1.5 hours) This would contribute around 147 g of CO_2-e for every full charge of the battery, or 8.2 g/mile. In order for an e-scooter to contribute as much GHG emissions from usage as it’s manufacturing and shipping, it would need to go through nearly 1500 charges if we use the high end of the manufacturing and shipping figures.

Now let’s compare those values with automobiles. Using Argonne National Lab’s Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) Model, the vehicle cycle (manufacturing and recycling) and fuel cycle (on road and fuel production) of emissions associated with different vehicle and fuel mixes can be effectively calculated (See table below). Manufacturing one vehicle alone emits as much GHG as 40 scooters. Even driving a cleaner automobile, such as an electric car, emits over 20 times that of an e-scooter. Driving a CAFE standards-compliant SUV 500 miles (two workweeks of a 50-mile round trip commute) would already emit more than the manufacturing and shipping of an e-scooter.  Clearly, the technology of e-scooters is not the problem, it is the associated emissions from their collection for charging where their environmental cleanliness gets beyond murky.

Emissions Factors of Various Automobiles Fuel Types

Source: GREET 2018 Models 1 & 2

Unlike non-electric shared dockless modes, scooters require charging. As noted above, the actual charging related emissions are minimal, but the scooters need to be collected by an individual using a type of vehicle to bring them to some location to charge. While there have been many amusing pictures and videos of several scooters being transported by haphazardly stacking them on top of each other to a charging location, circulating the media, this is hardly the norm. Instead, most scooters are collected using automobiles and, given recent trends, a light-duty truck, as opposed to a fuel-efficient car.

These “chargers” are paid for collecting, charging, and redistributing scooters to high use areas before morning commutes start. Chargers can maximize their profit by collecting as many scooters as possible in the smallest area, though, as with many other gig economy jobs, the competition can be fierce, with chargers undercutting each other. According to the authors of the scooter life cycle analysis, chargers can drive over 2.5 miles to collect one scooter on average (about 1200 g CO_2-e using our models).

Rebalancing is not a new issue for shared mobility options, docked or not. In Washington DC, Capital Bikeshare (the capital region’s major bikeshare service) moves over 1000 bicycles a day in work vans for redistribution. This is not exclusive to the capital region, and areas are trying newer more environmentally friendly options for relocating bicycles, such as this electric tricycle cart in Portland, OR and this bike trailer in DC.

Lyft, who own the bikeshare operator Motivate (DC’s Capital Bikeshare and NYC’s CitiBike) and runs their own Lyft branded scooters, is reportedly very interested in introducing docks to their scooter share system. This can serve as a charging station, removing a large portion of their lifetime emissions, and a central place to leave them, addressing citizen complaints. Docks may also help address issues of disaffected citizens setting them on fire and throwing them in lakes, which will help increase their lifespan beyond the reported 28.8 days.

While emissions per mile can be close to that of automobiles, this is mostly because automobiles are a part of the scooter-share system. Comparing total contributed emissions, automobiles with their longer lifespan and more absolute miles driven, produce significantly more emissions in their lifetime than a scooter. Scooters have the potential to reduce emissions, lessen congestion, and provide more convenient mobility options in the transportation sector, but these benefits will only be maximized if they can operate without requiring an automobile for redistribution.

Cities and micromobility companies can collaborate to create curbside parking (and solar-powered charging options) that will diminish clutter and provide convenient collection points. Cities can regulate the amount of charge required to charge scooters and companies can also institute incentive programs, such as Capital Bikeshare’s “Bike Angels” program, which rewards users for repositioning bikes at the end of their trips. While many other solutions exist, policies should be implemented to achieve a specified objective. If that objective is to emit less GHG, reducing extraneous automobile trips from micromobility is a good start.