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| Fig. 1: Both cars and bikes are used for transportation. (Source: Wikimedia Commons) |
As people look to cut their carbon footprint in an effort to reduce global CO2 emissions, using a bike instead of a vehicle for transportation has been touted as one way to make an impact, as shown in Fig.1. [1] Although biking has no tailpipe emissions, there are emissions associated with biking due to the calories needed to cycle, as well as the emissions associated with the bike itself. This analysis thus aims to take into account the total CO2 emissions associated with biking and driving to comprehensively compare the two options.
When considering the emissions associated with biking to work it's important to consider both the life cycle emissions of creating the bike and the emissions associated with powering the bike. In terms of lifecycle emissions, a study by Chen et al. found that producing a ride-share bicycle, including all the production materials, amounts to 26.4 kgs of CO2. [2] Energy and water used to produce the bike add about an extra 5 kg of CO2, while additional emissions associated with disposing of the bike bring the total to 34.56 kg of CO2 per bike. Assuming that a bike is able to last 19,200 km, this results in a lifecycle emission of 0.0018 kg of CO2 per km. [3]
One study found by the Wisconsin Department of Health calculated that a 70 kg person would burn 2.356 × 106 Joules per hour of biking at moderate speeds (5.36 - 6.21 m/s). [4] This means on average 113 Joules/m or 1.13 × 105 Joules/km are burned when cycling. Kolbe analyzed hundreds of meat-containing, vegetarian, and vegan recipes and found the related CO2 emissions per amount of energy. [5] Meat-containing, vegetarian, and vegan recipes averaged 7.07 × 10-7 kg CO2-eq/Joule, 2.72 × 10-7 kg CO2-eq/Joule, and 2.46 × 10-7 kg CO2-eq/Joule respectively. This means that kg CO2-eq per km can average between 0.0278-0.0800 kg/km. Including the life-cycle assessment of the bicycle, this brings the average to 0.0296-0.0818 kg/km.
In a 2018 study by Del Pero et al., the lifecycle emissions of battery electric vehicles (BEV) and internal combustion engine vehicles (ICEV) were compared among cars driven for 150,000 km. [6] This included production, energy used while operating, tail-pipe emissions, and end-of-life processing. Results indicate that BEV produces 0.1286 kg CO2-eq/km while the ICEV produces 0.2032 kg CO2-eq/km.
As discussed above the emissions associated with biking are 0.0296-0.0818 kg/km, depending on the diet of the user, while the emissions associated with driving are 0.1286 kg CO2-eq/km for battery electric vehicles and 0.2032 kg CO2-eq/km for internal combustion engines. In the United States the average daily distance traveled is around 30 km. This means on an average day, an American who is a meat eater and who drives an internal combustion engine, traveling by bike saves 3.642 kg CO2-eq in emissions. In comparison to a BEV, the emissions savings are only 1.404 kg CO2-eq. The savings can be increased by adopting a vegan diet, saving 5.208 kg CO2-eq in comparison to an ICEV or 2.970 kg CO2-eq in comparison to a BEV.
This comparison assumes one driver per mode of transportation. However, in the case of a meat-eating cyclist and ICEV, the emissions per person would be lower for the ICEV if had at least 3 people. For BEV this would be just two people. In the case of a vegan cyclist, the emissions per person would be lower for the ICEV if the car contained 7 people, while for the BEV this would be 5 people.
As shown in this analysis, overall, the emissions per person for a cyclist of any diet are lower than the emissions associated with driving a BEV or ICEV. However, this can depend on factors such as the processing of the bike and car, the speed of the trip, the weight of the cyclists, and more. An important conclusion of this study is that driving a BEV or ICEV can emit less emissions per person than a bicycle when carpooling.
© Kenzie Sanroman Gutierrez. The author warrants that the work is the author's own and that Stanford University provided no input other than typesetting and referencing guidelines. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
[1] D Bucher et al., "Energy and Greenhouse Gas Emission Reduction Potentials Resulting from Different Commuter Electric Bicycle Adoption Scenarios in Switzerland," Renew. Sustain. Energy Rev. 114, 109298 (2019).
[2] J, Chen et al., "Life Cycle Carbon Dioxide Emissions of Bike Sharing in China: Production, Operation, and Recycling, Resources", Resour. Conserv. Recycl. 162, 105011 (2020).
[3] T. Schutt, "How Much Carbon Does Cycling Really Save?" Physics 240, Stanford University, Fall 2022.
[4] A. Zhan et al., "Accurate Caloric Expenditure of Bicyclists Using Cellphones," in SenSys 2021: Proc. 10th ACM Conf. on Embedded Network Sensor Systems (ACM, 2012), p. 71.
[5] K. Kolbe, "Mitigating Climate Change through Diet Choice: Costs and CO2 Emissions of Different Cookery Book-Based Dietary Options in Germany," Adv. Clim. Change Res. 11, 392 (2020).
[6] F. Del Pero, "Life Cycle Assessment in the Automotive Sector: A Comparative Case Study of Internal Combustion Engine (ICE) and Electric Car," Procedia Struct. Integr. 12, 521 (2018).
