The three abbreviations say which stage of the energy is counted in transport emissions, and each gives a different figure for the same trip. The terms come from EN 16258:2012; EN ISO 14083, which replaced that standard in 2023, renamed them, and the GLEC Framework (v3.2, 2025) uses both sets of names.
| Boundary | ISO 14083 name | What it covers |
|---|---|---|
| TTW, tank-to-wheel | Operational emissions | Fuel burned or leaked at the vehicle, refrigerant leakage |
| WTT, well-to-tank | Energy provision emissions | Producing, storing and distributing fuel and electricity |
| WTW, well-to-wheel | Total emissions | The sum of both |
An electric vehicle burns no fuel, so the fuel share of its TTW is zero and the load moves to the WTT side, where the electricity is generated. A company that calculates only TTW therefore shows a misleadingly low figure; ISO 14083 and GLEC base reporting on total emissions, which is WTW.
On a refrigerated vehicle, the fuel used by the fridge unit and any refrigerant leakage go into TTW, while the electricity for a unit running on shore power goes into WTT. The figure is always given with its boundary: 120 kg CO2e (WTW, GLEC v3.2) is a complete line, and a figure without a boundary cannot be compared with another report.
