WLTP

The Worldwide Harmonised Light Vehicles Test Procedure, universally abbreviated to WLTP, is the standardised laboratory test used to measure a passenger car's or light van's fuel consumption, carbon-dioxide emissions and, for electrified vehicles, electric driving range. It exists because buyers, regulators and tax authorities all need a single, repeatable yardstick by which different models can be compared, and because the figures it produces feed directly into vehicle taxation, fleet-average emissions targets and the labels displayed in showrooms.

WLTP was developed under United Nations auspices to replace the New European Driving Cycle, or NEDC, which had become notorious for understating real-world consumption. The NEDC dated from the 1980s and used a gentle, unrealistic driving profile with long steady-speed sections and modest accelerations, so the gap between its quoted economy and what drivers actually achieved widened steadily as engines and cars evolved. WLTP was phased in for new European models between 2017 and 2019 specifically to narrow that gap.

Mechanically, the test is run on a rolling road, or chassis dynamometer, in a temperature-controlled laboratory, with the car's exhaust gases and energy use measured precisely throughout. The WLTP cycle is longer and faster than the old one, lasting around thirty minutes and covering roughly twenty-three kilometres at an average speed near forty-six kilometres per hour, with a higher top speed and brisker, more varied accelerations spread across low, medium, high and extra-high speed phases that better represent urban, rural and motorway use.

A significant improvement over NEDC is that WLTP accounts for factors that genuinely affect consumption on a given car. It is far more sensitive to vehicle mass, aerodynamic drag and rolling resistance, and crucially it considers optional equipment: larger wheels, panoramic roofs and other extras that add weight or drag can raise the certified figures. This means a heavily optioned car can carry a higher official CO2 number, and therefore a higher tax band, than the same model in basic trim.

Because even a thorough laboratory test cannot capture every real-world variable, WLTP is complemented by Real Driving Emissions testing, known as RDE. RDE uses portable measurement equipment carried on the car during actual driving on public roads, and is aimed chiefly at pollutants such as nitrogen oxides and particulates rather than at fuel economy. Together the two procedures bracket both laboratory repeatability and on-road reality.

It is still important to read WLTP figures as comparative benchmarks rather than guarantees, since individual results depend on driving style, climate, payload and route. The procedure relates closely to the NEDC it superseded, to RDE testing for pollutants, and to the underlying measures of fuel consumption and CO2 emissions that drive both consumer choice and regulatory compliance across much of the world.