The environmental impact of being transported from A to B is significant because transport is a major user of energy, and burns most of the world’s petroleum. The transport sector accounts for about 25% of global CO2 emissions, most of them coming from road traffic.
To bring more clarity to the ongoing sustainability debate, we collected as many available data points as possible from reputable sources to rank the various urban mobility modes—including the growing number of New Transportation services, such as e-scooters and shared bikes—based on their average carbon-emission output per passenger-kilometer.
Disclaimer: Our ranking is not illustrating scientifically proven results as the carbon emissions data per transport type is based on existing third-party research with varying methodologies and assumptions. We combined the data for a direct comparison but realize that it’s not a clean apples-to-apples comparison. However, the benefits outweigh the drawbacks as we hope this overview initiates more discussion and joint efforts among the most relevant travel and mobility providers to further slash CO2 emissions.
For exploring the data in more detail, here is the graphic in interactive Tableau format.
For full transparency, we listed all the studies and articles we referenced as well as the assumptions we applied in a separate Airtable:
Last but not least, below you find additional context for the categories we applied for breaking down total CO2 emissions into its major components.
The environmental impact caused by the direct operation of the vehicle is recorded. For example, direct emissions at the exhaust pipe, abrasion emissions from brake linings, wheels, road and overhead lines (for railways).
The environmental impact of indirect operation is determined, which primarily includes the provision of energy. This includes processes from energy extraction from the environment to delivery to the tank (“well-to-tank”). In the case of electrically-powered vehicles, the provision of energy comprises the processes of electricity production in the power plant via transport in high-voltage lines and transformation into the battery.
All the processes required to keep the vehicle roadworthy during its service life are counted. For example, changing the tires of cars and replacing consumables in railway trains. E-Vehicles, battery replacement is fully included in vehicle production and not in vehicle maintenance.
Manufacture & Disposal
This category includes all processes that affect the manufacturing of the vehicle that are not included in maintenance. In addition to the pure material costs, the energy costs and operating emissions of the production facilities are considered, as well as the professional disposal of the vehicles after the average service life has expired.
The construction, maintenance, and disposal of all types of tracks are counted. In the case of road transport, these include roads, car parks and major infrastructures such as tunnels or bridges. In the case of rail traffic, entire lines, safety walls, bridges, and tunnels fall into this cluster while in the case of air traffic, the airport’s infrastructure is considered.