NEDC is dead, long live WLTP
One year after WLTP became standard, Vicky Parrott explains why it’s better
The Worldwide harmonised Light-duty vehicles Test Procedure (abbreviated to WLTP) has been the industry standard for a year now. Designed to give a more realistic gauge of a car’s efficiency than the New European Drive Cycle (NEDC) that it replaces, WLTP is a more thorough way of testing new cars’ fuel econony and emissions.
Every model registered in the UK must now be homologated under WLTP, which is developed for global use but which is also subject to specific European regulations.
The outgoing NEDC test was implemented in the Eighties and became notorious for returning over-optimistic fuel economy and CO2 emissions figures that were virtually unachievable in real driving conditions.
As with the old NEDC test, the WLTP is carried out in a laboratory, but the test is
longer and more varied in order to be more representative of real-world driving. Developed using some 500,000 miles of real driving data gathered from drivers all around the world, the WLTP lasts 30 minutes and 14.4 miles, at an average speed of 28.9mph and a maximum of 81.3mph, allowing for temperature changes from 14 degrees C to 23 degrees C, with gearchange points differing depending on the vehicle, and a variety of driving phases including acceleration and braking. A car’s power-to-weight ratio also dictates variable factors in the test cycle.
By comparison, the NEDC test lasted 20 minutes and 6.8 miles, had fewer stops, and didn’t take into account optional equipment such as air-conditioning, as the WLTP does.
Roughly speaking, experts estimate that there is a disparity of as much as 20 per cent between figures attained under the NEDC and the WLTP, but of course it will vary. A VW Up GTI, for instance, achieves 110g/ km of CO2 and an economy of 49mpg (EU Combined) under NEDC rules, but testing under the WLTP regime sees those figures amended to 127g/km and 42mpg.
Electric cars have a considerable variation in official driving range between the two test formats, too. The Jaguar I-pace will cover 337 miles on a full charge under NEDC, or 298 miles under WLTP.
For car buyers, WLTP is a change for the good. It provides more relevant and comprehensive information that will allow for an informed buying decision. But even the most accurate tests won’t reflect every individual’s particular needs. Put simply, your mileage may vary.