Recently, there has a been a fair amount of discussion surrounding the environmental impact of e-scooters and e-bikes in cities around the world. I thought I would do a quick breakdown of the CO2 emissions, comparing trips taken by e-scooters to those that they are replacing.
A recently published paper in Environmental Research Letters by Hollingsworth et al. (2019) did some really interesting analysis of the greenhouse gas emissions produced by new e-scooters. The findings indicate that these scooters produce 125.5g of CO2/passenger kilometre (202g/passenger mile). Breaking this down, roughly 50% of the emissions are from the manufacturing of the vehicles, 43% come from collection and redistribution services, and only 4.7% from the electricity used in charging the vehicles. Interestingly, the lifespan of these scooters has been reported to be from 1 month to 2 years, depending on use, abuse, etc.
From a transportation planning perspective, a number of cities have been asking, “What modes of transportation are these services replacing?” Through a number of surveys at least five companies/cities have summarized their responses in reports (see references below). Sifting through these reports, I put together the table below (Table 1). While the numbers vary substantially, there are some common percentages.
| France | Portland | North Carolina | Denver | San Francisco | |
| Walking | 44% | 37% | 49% | 43% | 61% |
| Bicycle | 12% | 9% | 14% | 19% | |
| Public Transit | 30% | 10% | 11% | – | – |
| Car or ride-share | – | 34% | 34% | 32% | 14% |
| No Trip | – | 8% | 7% | – | 7% |
Table 1: The results of five surveys on micro-mobility services. Responses to the question, “What modes of transportation are these services replacing?”
For ease of analysis, I put together two scenarios. The first scenario estimates CO2 emissions by taking the average from each of the above surveys and normalizing the percentages to sum to 100%. The second scenario takes the maximum CO2 possible based on the results of the five surveys (e.g., maximum percentage of car trips, followed by bus, etc). These data are shown in the table below (Table 2). Column 3 of this table shows the CO2 emissions per vehicle per passenger kilometre as reported by the US Department of Transportation and US Environmental Protection Agency. Note that the value of 54g/km for biking is the cost of redistribution for a bike-share company and public transit trips have been split 50/50 into metro and bus use.
| Average | Max | CO2 (g/km) | Average CO2 (g/km) | Max CO2 (g/km) | |
| Walking | 41% | 17% | 0g | 0 | 0 |
| Bicycle | 12% | 19% | 54g | 6.48 | 10.26 |
| Public Transit (Metro) | 7.5% | 0% | 116g | 8.7 | 0 |
| Public Transit (Bus) | 7.5% | 30% | 183g | 13.725 | 54.9 |
| Car or ride-share | 26% | 34% | 251g | 65.26 | 85.34 |
| No Trip | 6% | 0% | 0g | 0 | 0 |
| Total | 100% | 100 | 94.2 | 150.5 |
Table 2: Calculations for the total amount of CO2 per km for the average breakdown of travel mode as well as the maximum estimated travel mode percentages.
In comparing the results of this analysis we find that for the Average Scenario (average of all 5 surveys) the CO2 emissions are 94.2g/km. For the Max Scenario (max CO2 of all 5 surveys) the CO2 emissions are 150.5g/km. Compare these values to the 125.5g/km for all trips as e-scooter trips.
Based on the average of five surveys, this equates to a surplus of 31.3g/km of CO2 produced by the introduction of these scooters into a city.
Disclaimer. I fully acknowledge that these numbers are rough estimates and I had to make some broad assumptions in put together this analysis. For example, most people will use their own bike instead of bike-share and I have split ridership 50/50 for public transit in the first scenario which is likely incorrect, but works as estimates for this analysis. Similarly, I only took into consideration the operation of a car, not the manufacturing. I also did not take into consideration the make/model/year of the e-scooter, etc.
References
6-t (2019). 2019 usages et usagers des trottinettes electriques en free-floating en france. Technical report, 6-t. https://6-t.co/en/free-floating-escooters-france/
Chang, A., Miranda-Moreno, L., Clewlow, R., and Sun, L. (2019). Trend or fad? Deciphering the enablers of micromobility in the u.s. Technical report, SAE International. https://www.sae.org/binaries/content/assets/cm/content/topics/micromobility/sae-micromobility-trend-or-fad-report.pdf
DCC (2019). Electric scooter data & survey results. Technical report, Denver City Council. http://denvergov.org/content/denvergov/en/denver-council-district-13/news/2019/electric-scooter-data—survey-results-.html
Hollingsworth, J., Copeland, B., and Johnson, J. X. (2019). Are e-scooters polluters? the environmental impacts of shared dockless electric scooters. Environmental Research Letters, 14(8) :084031. https://iopscience.iop.org/article/10.1088/1748-9326/ab2da8
Lime (2018). Lime : San francisco scooter use survey results. Technical report, Lime. https://www.li.me/hubfs/Lime%20San%20Francisco%20Scooter%20Survey%20Findings.pdf
Portland Bureau of Transportation (2018). 2018 e-scooter pilot survey results. Technical report, Portland Bureau of Transportation. https://www.portlandoregon.gov/transportation/article/700916
U.S. DOT (2010). Public transportation’s role in responding to climate change. Technical report, U.S. Department of Transportation. https://www.transit.dot.gov/sites/fta.dot.gov/files/docs/PublicTransportationsRoleInRespondingToClimateChange2010.pdf
U.S. EPA (2010). Greenhouse gas emissions from a typical passenger vehicle. Technical report, U.S. Environmental Protection Agency. https://nepis.epa.gov/Exe/ZyPDF.cgi?Dockey=P100U8YT.pdf