WLTP: What it means for MPG figures

WLTP is designed to give more realistic mpg figures. But what exactly is it and does it work?

  • WLTP meaning explained
  • How the WLTP test works
  • Why WLTP should mean more accurate mpg figures

What is WLTP?

WLTP stands for the Worldwide Harmonised Light Vehicles Test Procedure. Since September 2017, all new cars have been tested for fuel economy under WLTP.

This test provides the claimed fuel economy figures for new cars that manufacturers use in their brochures and websites.

WLTP replaces the old NEDC test. Although WLTP is designed to be more reflective of real world driving conditions, it is still a laboratory-based test.

While it creates a more accurate driving profile, it can't account for variations in weather, car occupancy and traffic congestion - all of which have a big effect on fuel economy.

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Will it mean more realistic MPG figures?

In theory yes. The WLTP test is longer, changing from the previous 20 minutes to 30 minutes and the test starts at a temperature of 14°C rather than the old NEDC levels 20°C to 30°C, a better representation of the UK climate.

It also covers more than twice the distance - 14 miles at a higher average speed - and includes more braking and accelerating to reflect situations that drivers experience in everyday life. Extra weight and power used by optional equipment are now taken into account as well.

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What is NEDC?

The New European Driving Cycle was designed in the 1980s when cars were lighter, less powerful and fitted with less equipment.

The old NEDC test required a car to drive through an urban cycle accelerating then decelerating to idle a certain number of times, to a maximum 31mph and averaging out at 12mph.

The extra-urban cycle had an average 39mph speed and a peak 75mph, over a shorter distance. Combined they covered just under seven miles and took 20 minutes. The measurements for each were used to calculate an average – the car’s official average fuel consumption figure.

The NEDC quickly became outdated and was creating unrealistic fuel economy figures. This was one of the reasons we launched Real MPG, to give drivers realistic mpg figures.

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WLTP v NEDC - the differences

  WLTP NEDC
Starting temperature Cold Cold
Cycle time 30 mins 20mins
Idle time 13% 25%
Cycle length 14.5 miles 6.8 miles
Average speed 29mph 21mph
Maximum speed 81mph 75mph
Temperature 20C - 30C 14C

There are also different test phases. The WLTP has low, medium, high, extra high (combined), plus a 'city' test for EVs and PHEVs. The NEDC was simply an urban and extra urban test, the average of which created a combined figure.

WLTP also takes into account extra equipment fitted to a car and its influence on weight, aerodynamics, power and rolling resistance. 

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When did it change?

The switch from NEDC to WLTP had several phases. From September 2017, all new model introductions were subject to WLTP type approval.

Then from September 2018, all new sales received type approval under WLTP. A year later, in September 2019, all new registrations became subject to Real Drive Emissions testing (RDE).

The RDE test measures pollutants, such as NOx, emitted by cars while driven on the road. RDE does not replace the WLTP test but sits alongside it. 

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Does WLTP affect CO2-based tax?

Previously, each car received a certificate of conformity which showed its CO2 emissions level based on the NEDC. During the transition from NEDC to WLTP, cars approved before then will continue to have CO2 values as measured under the current NEDC test only.

Since September 2017, when a new car is certified, its official documents will have CO2 emission values from the new WLTP test.

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