What is a billion-passenger-kilometer?

Answer 1

A passenger-kilometer (pkm) is the product of the distance a vehicle travels times the number of occupants travelling that distance. (A billion passenger-kilometers would be 1'000'000'000 pkm). For example: 250 passengers travelling 1000 kilometers in a plane will give us 250'000 passenger-kilometers. This unit is used to compare the fuel consumption or CO2 emissions of different means of transport that carry different amounts of passengers, or the same means of transport at different levels of occupancy. For example: A plane with a 128 seat capacity and all seats occupied will emit a bit more than 10 tonnes of CO2 to travel 1000 kilometers. This corresponds approximately to 10'000'000grams of CO2 for 128'000 passenger-kilometers, 10'000'000gCO2 / 128'000pkm = 78gCO2/pkm. The same plane half full would correspond to half the passenger-kilometers (64000pkm) and therefore double the emissions per passenger-kilometer (156gCO2/pkm). A standard petrol fuelled car with 4 passengers would emit about 150kg of CO2 to travel the same distance. This would correspond to 38gCO2/pkm. The same car with only 2 passengers would have emissions comparable to the full plane above at 76gCO2/pkm. The figures used in these examples were adapted from those given by the web site: www.travelfootprint.org.