In order to measure how much fuel or electricity a car consumes and whether it complies with the exhaust emission limits, the legislator prescribes standardized test procedures. Since September 1, 2017, the new “Worldwide Harmonized Light-Duty Vehicles Test Procedure” (WLTP) has been in force throughout the EU for the type approval of new passenger cars. It follows on from the NEDC (New European Driving Cycle), which has been in force since 1992. WLTP comprises both a new driving profile on test benches and more precise and up-to-date framework conditions for the entire test and is intended to lead to more realistic consumption data than was the case with the previous measuring procedure.
WLTP to map driving behaviour more realistically
Information on consumption or range is to be determined on the basis of an objective and reproducible test procedure. Exactly defined conditions should make it possible to compare different models. The values determined should be as representative as possible of the current driving behaviour of people in road traffic. The NEDC procedure used so far in Europe no longer met this requirement. It was developed in the 1990s primarily for the measurement of pollutant emissions as a theoretical test drive. The new WLTP, on the other hand, is based on empirically collected real driving data of routes in Asia, Europe and the USA and is therefore much more representative.
Even WLTP cannot take all factors into account
The fuel consumption of a car is also essentially determined by the driving resistances – i.e. mass, air resistance and rolling resistance. WLTP considers these physical driving resistances better and more comprehensively than NEDC. However, even a representative bench test such as the WLTP cannot take into account all factors that influence fuel consumption in reality. Among the most important factors that increase fuel consumption, which a laboratory test can only record with difficulty, are the individual driving style, the geographical conditions of the route, the load, the climatic conditions and the use of energy for auxiliary consumers such as seat heating or air conditioning.
Electric vehicles are tested according to WLTP
Electrified vehicles must also be tested in Europe according to the new WLTP rules in order to obtain type approval. Just as the consumption figures for vehicles with internal combustion engines are changing due to the introduction of the WLTP, the same applies to the range figures for purely electric cars and plug-in hybrid vehicles. With the WLTP, the range specifications become more representative.
Even though WLTP cannot map the entire range of actual vehicle use, the new procedure offers a better information basis for car purchases due to a greater realism of its results.