The CO2 footprint of your trip is calculated as: the distance of your trip multiplied by the CO2 emissions of a passenger for the different means of transport, per kilometer. It concerns only the main part of the route and does not take into account the transport from / to the station or airport.
Average emissions for a passenger per kilometer:
3,4 g of CO2 per kilometer
205 g of CO2per kilometer
168 g of CO2 per kilometer
Source Trains Renfe-SNCF en coopération (TGV): Actual frequencies and electric consumption 2012 of each carrier;
Electricity transmission factor for "Europe" (420gCO2 / kWh) or electricity emission factors for railway electricity from the countries concerned when they were transmitted by traction electricity providers, for kilometers in others countries.
Source Cars: Average use of particular cars France: Ministry of Sustainable Development and Energy - Observation and Statistics Service (SOeS), Cars’ average consumption in France and fuel emission factors: ADEME - Carbon Base
Source Airplanes: Ministry of Sustainable Development and Energy "Information CO2 transport services - Methodological Guide" 2012 - For a 150-seat airplane performing a flight of less than 1000 km.