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Fleet FAQ

Q:

What are the different types of mpg figures (WLTP, NEDC)?

A:

To determine the miles per gallon (mpg) figure - and inform you of how economical it is to run - each new vehicle goes through a testing procedure.

From September 2017 a new testing regime began to be used.

This is called WLTP, or the Worldwide Light vehicle harmonised Testing Procedure. It replaces the NEDC lab test introduced in the 1980s.

The difference between them?

  • NEDC is a single, 20 minute test cycle - WLTP a dynamic cycle of 30 minutes
  • There are two phases to NEDC over 11 kilometres at an average speed of 24kph, WLTP is four phased over 23km and an average of 47kph..
  • Crucially, unlike NEDC, WLTP considers additional features, or optional equipment. Their impact on CO2 emissions and fuel economy were not part of the NEDC test.

 

WLTP will introduce much more realistic testing conditions. These include:

  • More realistic driving behaviour;
  • A greater range of driving situations (urban, suburban, main road, motorway);
  • Longer test distances;
  • More realistic ambient temperatures, closer to the European average;
  • Higher average and maximum speeds;
  • Higher average and maximum drive power;
  • More dynamic and representative accelerations and decelerations;
  • Shorter stops;
  • Optional equipment: CO2 values and fuel consumption are provided for individual vehicles as built;
  • Stricter car set-up and measurement conditions;
  • Enables best and worst-case values on consumer information, reflecting the options available for similar car models.

Because of all these improvements, WLTP will provide a much more accurate basis for calculating a car’s fuel consumption and emissions.

This will ensure that lab measurements better reflect the on-road performance of a car.

CO2 targets that car manufacturers have to meet by 2021 are based on the old NEDC test, the so-called New European Driving Cycle.

From the introduction of WLTP in September 2017, the WLTP-CO2 values will be translated back to NEDC-equivalent values to monitor compliance against the CO2 targets set by the European Union.

A ‘correlation exercise’ was carried out by the European Commission to determine how the values for new cars measured on the WLTP cycle will be translated back to NEDC equivalent values for monitoring against the EU CO2 targets.

These correlated NEDC values will either be calculated using a correlation simulation tool or based on the results of physical NEDC test.

The correlation tool has limitations that may result in higher NEDC-CO2 values.

If the correlation tool does not confirm a manufacturer’s declared CO2 value or the tool is not able to deal with specific technologies, CO2 values from the correlation exercise can be replaced by physically measured values using NEDC.

However, since this will be an updated version of NEDC (with tightened test set-up conditions), new cars that are type-approved under WLTP will have WLTP-CO2 values as well as higher (updated) NEDC-CO2 values compared to the current NEDC.

Source: WLTP Facts

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