When a truck brochure quotes an official CO2 figure, the number did not come from a driver with a stopwatch on the M6. It came out of a computer simulation with a legal framework around it, and operators comparing one manufacturer’s figure with another’s should know what the machinery behind those numbers actually is - because it determines how much weight the comparison can bear.
In Great Britain, heavy-duty CO2 and fuel consumption requirements sit inside the GB type approval scheme, based on retained Regulation (EC) 595/2009 and its implementing regulations - Regulation (EU) 582/2011 for emissions measurement and Regulation (EU) 2017/2400 for the determination of CO2 emissions and fuel consumption of heavy-duty vehicles and their components. The Vehicle Certification Agency administers the GB scheme, and its guidance states that type approval covering the determination of CO2 emissions and fuel consumption is required as part of GB type approval under the retained 2017/2400 requirements.
The scope matters to buyers. The retained regulation covers N2 vehicles with a technically permissible maximum laden mass exceeding 7,500kg and all N3 vehicles - rigid trucks over 7.5 tonnes and the heavy end - with exemptions for off-road, special purpose and multi-stage vehicles. Buses and trailers are not within scope of the GB requirements at this time. So the tractor unit and the 18-tonne rigid come with regulated CO2 determination; the trailer behind them does not.
The figures are produced by simulation. Manufacturers of vehicles in scope must hold GB type approval for a “License to Operate the Simulation Tool” - and the tool is VECTO, the Vehicle Energy Consumption calculation Tool. VCA’s guidance says manufacturers should continue to use the latest versions of the VECTO simulation tool and its subsidiary calculation tools for component data as per EU requirements, and simulations run on the latest versions will be accepted for GB type approval. Manufacturers may also indefinitely continue to use their EU component certifications - covering engines, transmissions, air drag and the rest - as inputs to their GB vehicle simulations.
That architecture has a direct consequence for how operators should read official figures: the declared number reflects the vehicle as simulated - its certified components, its configuration, the standard cycles in the tool - not any particular fleet’s routes, loads or drivers. Two trucks compared on official figures are compared on a level, regulated playing field, which is genuinely useful at purchase time. A single truck’s figure compared against your own telematics is a different exercise, and the gap between simulation and your duty cycle is information, not an accusation.
A simulation regime only works if manufacturers keep it honest, and the scheme builds in the checks. VCA says manufacturers holding the GB License to Operate are subject to legislated conformity of production provisions, including quarterly assessments of the simulation process and an annual verification testing procedure. The annual VTP testing does not need to be witnessed by VCA or its designated technical services, but the test data and reporting are reviewed by VCA’s conformity of production department as part of ongoing compliance assessment - and VTP testing can be conducted on EU vehicles and combined with EU approval activity where specifications are common to both markets.
For the operator, the takeaway is that the declared figure has an audit trail behind it: certified components, a licensed simulation process, quarterly process assessments and annual verification testing, all reviewed by the approval authority. That is a great deal more structure than a marketing claim, and somewhat less than a promise about your own fuel bill.
The CO2 regime does not sit alone. The same VCA guidance confirms that retained legislation sets the current heavy-duty emissions type approval requirement in Great Britain at Euro VI-D level, with evidence of compliance required at application - and vehicles, components or separate technical units tested to Euro VI-E for EU or other markets are deemed to comply with the GB Euro VI-D requirement. UNECE type approvals offer an alternative route, with a set of approvals to the listed UN regulations demonstrating equivalence to the retained GB standards. The operator’s version of all this is simple: a new truck sold for GB use arrives with a documented emissions level and a regulated CO2 and fuel consumption determination, both sitting inside an approval system that keeps auditing after the sale.
The sensible fleet use of VECTO-based figures is comparative and contractual. Comparative: when shortlisting trucks, the official CO2 and fuel consumption figures are the one dataset where every manufacturer has been measured the same way, so differences between them mean something. Contractual: as CO2 reporting creeps into customer tenders and emissions schemes, knowing that the truck’s regulated figure exists, what regulation produced it and what scope it covers puts the fleet in charge of its own data story. The trucks over 7.5 tonnes carry the regulated determination; remember what sits outside scope, and read the simulation for what it is - a rigorous, audited standard test, not your next fuel card statement.