Transportation: The Elephant on the Plane When I started tracking my carbon footprint, one category dominated all others: transportation. Specifically, aviation. This post breaks down the carbon costs of different transport modes and explores the uncomfortable mathematics of modern travel. The Numbers Carbon Emissions by Mode Per passenger per kilometre (kg CO2e): Mode Short Distance Long Distance Walking/Cycling 0 0 Electric train 0.006 0.004 Diesel train 0.041 0.028 Bus 0.089 0.