You can now find emission estimates and comparisons between different transport modes.
How we estimate carbon emissions
To calculate emissions for trains, Google uses a method that considers the distance travelled and the number of passengers in your search. According to the International Energy Agency (IEA), trains emit 19 grams CO2e lifecycle emissions per passenger kilometre on average. Exact emissions depend on the train and operator. IEA's data is updated annually and Google is working to source accurate information from train operators.
Train emissions compared to flying and driving
Google labels trains as 'climate friendly' because compared to flying the same distance, taking the train typically saves around 85% carbon emissions per passenger. Compared to driving the same distance, taking the train typically saves around 87% carbon emissions per passenger. The exact emissions savings depend on the train. Long-distance trains may save even more.
| Transportation mode | Emissions factor | Source |
| Train | 19 grams CO2e lifecycle emissions per passenger kilometre |
According to IEA |
| Plane | 123 grams CO2e lifecycle emissions per passenger kilometre |
According to IEA |
| Car (small/medium) | 148 grams CO2e lifecycle emissions per passenger kilometre |
According to IEA |
What are CO2e lifecycle emissions?
CO2e stands for 'carbon dioxide equivalent' and is an industry measure used to describe various greenhouse gasses based on their global warming potential. It is a common unit that is used to standardise the comparison of different greenhouse gas emissions. CO2e is calculated by converting measurements of other gases into equivalent amounts of carbon dioxide with the same global warming potential.
Lifecycle emissions are the aggregate, end-to-end quantity of emissions from fuel usage. This includes the direct emissions from fuel usage, as well as the emissions produced during each stage of fuel production.