WLTP : Worldwide Harmonised Light-Duty Vehicles Test Procedure

Added: 11 July 2019

1. What is WLTP and how does it work?

The old lab test - called the New European Driving Cycle (NEDC) - was designed in the 1980s. Due to evolutions in technology and driving conditions, it became outdated. The European Union has therefore developed a new test, called the Worldwide Harmonised Light Vehicle Test Procedure (WLTP). The EU automobile industry welcomes the shift to WLTP and has actively contributed to the development of this new test cycle.

While the old NEDC test determined test values based on a theoretical driving profile, the WLTP cycle was developed using real-driving data, gathered from around the world. WLTP therefore better represents everyday driving profiles.

The WLTP driving cycle is divided into four parts with different average speeds: low, medium, high and extra high. Each part contains a variety of driving phases, stops, acceleration and braking phases. For a certain vehicle type, each powertrain configuration is tested with WLTP for the vehicle's lightest, most aerodynamic (most economical) and heaviest, least aerodynamic (least economical) version.

2. What's the timeline?

Passenger vehicles (M type and Category N1 (i))

- From 1st September 2017, all new model instructions were subject to WLTP type approval and Real Driving Emissions (RDE) testing

- From 1st September 2018, all new sales received type approval under WLTP

- From 1st September 2019, all new registrations will be subject to RDE testing

- Light Commercial Vehicles (Categories N1 (ii), N1 (iii) and N2)

- From 1st September 2018, all new Light Commercial vehicle model introductions were subject to WLTP type approval and Real Driving Emissions (RDE) testing

- From 1st September 2019, all new sales of Light Commercial Vehicles will have received type approval under WLTP and all new registrations will be subject to RDE testing

3. What are the benefits of WLTP?

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

- More realistic driving behaviour

- A greater range of driving situations; low, medium, high, extra high and combined

- 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/energy consumption are provided for individual vehicles as built

- Stricter vehicle set-up and measurement conditions

- Enables best and worst-case values on customer information, reflecting the options available for similar vehicle models

- Add fuel/energy in all areas

Because of all these improvements, WLTP aims to provide a much more accurate basis for calculating a vehicle's fuel/energy consumption and emissions. This will ensure that lab measurements better reflect the on-road performance of a vehicle. Only compare fuel/energy consumption and CO2 figures with other vehicles tested to the same mechanical procedures. These figures may not reflect real life driving results, which will depend upon a number of factors including the accessories fitted (post-registration), variations in weather, driving styles and vehicle load.

4. What is NEDC?

The standardised NEDC applied for all passenger vehicles and light commercial vehicles. It was introduced by the European Union in 1992 in order to provide comparable values for fuel/energy consumption.

5. NEDC vs. WLTP

WLTP replaces the NEDC measuring procedure. New test parameters target more realistic values. See below how the procedures differ:

Conditions NEDC WLTP
Test duration 20 min. 30 min.
Test distance 11 km 23.5 km
Time spent stationary 25% 13%
Test phases Urban/Extra-urban, (combined)
Low, Medium, High, Extra high, (Combined); (plus “City” for electric vehicles and vehicles with plug-in hybrid drivetrain)
Speed Average: 34 km/h
Maximum: 120 km/h
Average: 46.6 km/h
Maximum: 131 km/h
Temperature 20-30° C
Cold engine start
14° C
(tested at 23° C corrected for 14° C)
Cold engine start
Special equipment options Not taken into consideration All equipment options are considered in terms of their influence on aerodynamics, weight and rolling resistance


6. What is the "Real Driving Emissions" (RDE) test and how does it work?

The Real Driving Emissions (RDE) test measures the pollutants, such as NOx, emitted by passenger vehicles while driven on the road. RDE does not replace the WLTP laboratory test, but complements it. RDE ensures that passenger vehicles deliver low emissions over on-road conditions. Europe is the first region in the world to introduce such testing, marking a major leap in the testing of vehicle emissions.

7. How do RDE tests work in practice?

Under RDE, a vehicle is driven over a wide range of real world driving conditions. Specific equipment installed on the vehicle collects data to verify that legislative caps for pollutants such as NOx are not exceeded.

Conditions include:

- Low and high altitudes

- Year-round temperatures

- Additional vehicle payload

- Up and down-hill driving

- Urban roads (low speed)

- Rural roads (medium speed)

- Motorways (high speed)

8. What equipment is used for RDE tests?

To measure pollutant emissions as the vehicle is being driven on the roads, vehicles are fitted with Portable Emission Measuring Systems (PEMS) that provide a complete real-time monitoring of the key pollutants emitted by the vehicle (i.e NOx).

The PEMS used for regulated emissions are complex pieces of equipment that integrate advanced gas analysers, exhaust mass flow meters, weather station, Global Positioning System (GPS) and a connection to the vehicle networks.

There is no 'standard' PEMS equipment and equipment manufactured by different suppliers will always deliver slightly different results. The collected data is analysed to check that the RDE trip boundary conditions were achieved and that the emissions were within acceptable levels.

9. When was RDE implemented?

RDE step 1 (with a NOx conformity factor of 2.1) has applied since 1 September 2017 for new vehicle types. It will apply to all types as of September 2019.

RDE step 2 (with a NOx conformity factor of 1.0 plus an error margin of 0.5) applies from January 2020 for new types and then from January 2021 for all types.

10. What are conformity factors?

A conformity factor is defined as a 'not to exceed limit' that takes into account a margin for error, which is present simply because the PEMS equipment does not deliver exactly the same results for each test. For example, PEMS are not as accurate as a full laboratory sytem so they will not measure to the same level of repeatable accuracy as a lab test. In practice, vehicle manufacturers must set their design objectives well below the legal limit to be certain of complying.

11. What is the link between the CO2 emissions and fuel/energy consumption of my vehicle?

The amount of CO2 a vehicle emits is directly related to the amount of fuel/energy it consumes. For instance, a diesel car emitting 95g CO2 per kilometre consumes around 3.7 litres of fuel per 100km, while a petrol vehicle consumes around 4 litres/100km for the same CO2 emissions.

Fuel/energy efficiency, sometimes referred to as fuel/energy economy, is the relationship between the distance travelled and the fuel/energy consumed. 

12. How will the implementation of WLTP affect vehicle tax?

The CO2 emissions figure is used to determine the cost of Vehicle Excise Duty ('vehicle tax') for new passenger vehicles during their first year of registration, in addition to any Company Vehicle Tax. For those passenger vehicles approved under WLTP, a figure equivalent to what would have been achieved had the vehicle been tested under NEDC will be used for taxation purposes - this is known as the NEDC equivalent value. From the 6th April 2020, the CO2 value obtained under WLTP will be used instead of the NEDC equivalent. When WLTP does start to be used to calculate vehicle tax, it will only affect passenger vehicles that at that time are unregistered, i.e. the CO2 figure that is used for tax purposes when the vehicle is first registered will not change during its lifetime.

13. What does WLTP mean for me?

The new WLTP testing regime is still a laboratory-based standardised test but it seeks to provide more realistic testing conditions and a more accurate basis for assessing a vehicle model's fuel/energy consumption and emissions figures. In essence, the aim is to ensure that test conditions better reflect real world driving. 

14. Will the model portfolios of Mercedes-Benz change?

No. At present no changes to the model portfolio are planned, however certain engine and gearbox combinations will change. Individual models and their engines will have to be further engineered in order to achieve even higher efficiency and reduce emissions as per the regulations. However, models will not be discontinued as a result of WLTP. 

15. Are there other procedures?

Yes, there are. The driving cycles for exhaust and consumption measurement developed in Japan (JC 08) and the USA (FTP 75) are more closely oriented on specific situations on the country's roads. For example, Japan's driving cycle includes numerous stop-and-go phases and is carried out twice, once as a cold start and once as a warm start. 

16. Does WLTP also apply to electric vehicles?

Yes, electric vehicles must also be tested according to the new WLTP rules. 

17. What will change on vehicle labelling and when?

From 1st January 2019, energy efficiency labels displayed alongside vehicles in showrooms will show a range of WLTP values for fuel/energy consumption (low, medium, high, extra high and combined) and a combined NEDC equivalent value (derived from the WLTP test) for CO2. 

Useful links

https://www.lowcvp.org.uk/initiatives/fuel-economy/wltp.htm

https://www.vehicle-certification-agency.gov.uk/fcb/wltp.asp

https://www.smmt.co.uk/industry-topics/emissions/testing/

https://www.gov.uk/search?q=wltp

http://wltpfacts.eu/what-is-wltp-how-will-it-work/

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