CO2 emissions: key differences between the NEDC cycle and the new WLTP cycle

Since September 2018, cars that previously had CO2 emissions within legal limits have seen those emissions increase by between 15% and 20% compared with before that date. The same car, therefore, if it had emissions of 100 g/km of CO2, from that date onwards recorded emissions of between 115 and 120 g/km. Why does this happen? The responsible party for this change is the pollutant emissions measurement system.

Before September 2018 the NEDC cycle was used, which was the standard for the automotive industry. Given everything that happened with the dieselgate scandal of Volkswagen, the authorities wanted to be tougher and began to analyse how to make measurements more reliable and prevent tricks used to disguise emissions. This is how the WLTP cycle was born, and it is the one that has changed the values of the measurements.

Difference between NEDC and WLTP

The NEDC and WLTP cycles have differences between them that make the measurements change substantially. In the NEDC cycle the tests were carried out in a closed laboratory, with the car placed on rollers that allowed it to run without moving from the spot. The maximum speed at which the tests were carried out was very low and did not provide all the information needed to properly assess the level of pollutant emissions.

With the WLTP cycle the tests are carried out in a real driving environment, on the road. This type of test records different amounts of pollutant gases, because the car is subjected to tests that simulate the common use of the car, so the records are much closer to reality. In addition, the maximum speed at which these tests are carried out reaches 120 km/h.

The test conditions mimic real driver behaviour, so consumption and the pollutant emissions produced by the car can be assessed more accurately. With the WLTP cycle we find that actions against the most polluting vehicles have been tightened, which with the NEDC cycle may have passed as low-polluting cars but now exceed the imposed limits.

In this way, a legislation more in line with reality can be implemented and significant discrepancies between the CO2 figure declared by the manufacturer and the one the vehicle actually produces can be avoided. The pollution caused by the car fleet is significant, although it is already known to be only one part of the larger pollution problem.

The use of fossil fuels in aviation, maritime transport and electricity generation is far greater than the pollution produced by vehicles, although any action taken in this regard can benefit everyone. Manufacturers are working to reduce pollutant emissions across all models, so the investment devoted to this multiplies every year. Engines are becoming increasingly efficient, although some things still need to change.

Buyer mentality is also important, since one only needs to look at the types of vehicles that are selling most at present. These are SUVs and other crossover vehicles, which have higher consumption and are less aerodynamically efficient, and therefore generate more pollutant emissions. The WLTP cycle will force brands to work harder in this direction and make those vehicles that are impractical in terms of emissions increasingly better.