Tank-to-Wheel (TTW)
Tank-to-wheel (TTW) emissions are the greenhouse gases produced when a fuel is combusted in a vehicle or piece of equipment — covering the stage from the fuel tank to the energy output. TTW is the direct combustion emission, corresponding to Scope 1 for company-owned sources.
What is Tank-to-Wheel (TTW)?
Tank-to-wheel (TTW) emissions refer specifically to the greenhouse gases released during the combustion of fuel in an engine or piece of equipment. The term originates from transport analysis and describes the "last mile" of a fuel's lifecycle — from the vehicle's fuel tank through the engine to the wheels (or, more broadly, to the useful energy output).
TTW is the counterpart to well-to-tank (WTT). Together, they form the well-to-wheel (WTW) lifecycle of a fuel. WTT covers the upstream supply chain emissions (extraction, refining, distribution). TTW covers the point-of-use emissions (combustion). WTW = WTT + TTW.
For carbon accounting, TTW emissions from company-owned vehicles and equipment are classified as Scope 1 direct emissions. These are the emissions produced when petrol, diesel, LPG, CNG, or other fuels are burned in the engine. The DEFRA emission factors for vehicle fuels (in kgCO₂e per litre or per km) represent TTW emissions.
For electric vehicles, TTW emissions are zero at the point of use — no fuel is combusted and no exhaust gases are produced. However, the emissions shift to Scope 2 (electricity generation) and Scope 3 (WTT of the electricity's input fuels, plus T&D losses). This is why a well-to-wheel comparison is important for comparing the total climate impact of EVs versus internal combustion vehicles.
The TTW/WTT distinction matters for accurate scope classification. When an organisation reports its fleet emissions using DEFRA's per-litre fuel factors, it captures the TTW (Scope 1) component. To capture the full lifecycle impact, it must separately add the WTT (Scope 3 Category 3) component. Some organisations report only TTW for simplicity; comprehensive reporting includes both.
Practical Examples
A delivery company's van burns 10,000 litres of diesel annually — the TTW emissions are approximately 25.1 tCO₂e (Scope 1), calculated using the DEFRA direct combustion factor for diesel.
An electric vehicle fleet has zero TTW emissions because no fuel is combusted in the vehicles. The associated emissions are instead reported as Scope 2 (electricity) and Scope 3 (WTT and T&D losses).
A well-to-wheel comparison shows that a diesel car produces approximately 3.1 kgCO₂e per litre WTW (2.51 TTW + 0.62 WTT), while an equivalent EV charged from the UK grid produces approximately 0.05 kgCO₂e per km — demonstrating the carbon advantage of electrification.
How Climatise Helps
Climatise calculates both TTW (Scope 1) and WTT (Scope 3) emissions from your fleet fuel data, giving you the complete well-to-wheel picture. For mixed fleets with both ICE and electric vehicles, the platform correctly allocates emissions to the right scope for each vehicle type.
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