Stricter testing procedures are set to provide UK car buyers with more accurate fuel economy and emissions information from today (01 September). Two new test regimes come into force - WLTP and RDE - with both providing more accurate data than the existing NEDC test that is widely regarded as unfit for purpose.
It is because of the New European Drive Cycle's (NEDC's) lack of realistic testing that drivers often cannot come close to their car's quoted fuel economy figure. The gap between quoted official figures, and those found in the real world has been increasing from an average of around 7% a decade ago to over 40% in 2017.
To improve the accuracy of the data, the Worldwide Harmonised Light-Duty Vehicles Procedure (WLTP) cycle and Real Driving Emissions (RDE) tests have been developed. The WLTP, which has been in the pipeline for over a decade, provides data obtained in a similar way as NEDC, but with more realistic drive cycles.
Both the NEDC and WLTP test are conducted on a 'rolling road' in laboratory conditions; though the WLTP is a longer test, and with a greater degree of variance in drive cycles. For example, engine speeds are changed more often, with greater variance in the acceleration and braking phases. Likewise, more load is put on the engine, there are more gear changes, and a greater range of temperatures are taken into account.
The new WLTP drive cycles are based on analysing half a million miles of real driving data, and more accurately reflect the fuel economy and emissions figures actually found by drivers. However, during the time it has taken to agree globally, the WLTP has itself become outdated with some analysts estimating that it will continue to differ from most real world. It is also designed for all global regions rather than being closely matched to any one country's driving style.
Comparing the NEDC and the WLTP figures, Jelica Pavlovic and colleagues based at the EC's Joint Research Centre have concluded that: "WLTP-based CO2 figures will be around 15% higher than the current type approval values, potentially halving the current gap between type-approval and in-use fuel consumption". In other words, while an improvement, the WLTP data will still not match most drivers experience of their car's CO2 emissions or fuel economy.
True, although with a 40% lab V's real world fuel economy gap, this has been long overdue. Every car I've bought I've looked at the MPG figures to get an idea of running costs, from now on, I'll have a better understanding and far more realistic idea of fuel efficientcy of every car I buy in the future.