The US tests are far more realistic than the NEDC tests, which are highly flawed and easily manipulated. Some manufactures are now rolling out their "fuel economy calculators" where you can select your car/engine, driving style, average trip distance, whether you carry passengers etc and they give you an estimate. Pretty cool. Example below based of Peugeot 308 station wagon 1.6 HDI:
"Estimated average real-world fuel consumption 57.6 MPG"
You can even change the wheel size, as this makes a difference, percentage of rural/urban/highway driving etc. Check them out here:
Consumption Calculator
Consumption based on usage
Vehicle consumption | Real use figures | - Citroën UK
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