The WLTP deviates in some details from the NEDC, affecting the determination of the official EU type-approval emission values. This also has consequences for the NEDC-based CO₂ passenger cars’ emission target for 2020/2021 (95 gCO₂/km), which will have to be adapted to the new testing procedure, the ICCT team writes. The new ICCT working paper identifies the main influencing parameters and quantifies the impacts.

Although many WLTP parameters, given their different definitions from the NEDC, will have no potential impact on CO₂, there are three key elements with different definitions that should be considered for the derivation of a WLTP-NEDC conversion factor for CO₂ emissions, according to the ICCT report:

1. A longer and more dynamic driving cycle, including a more flexible gear shift strategy for manual transmissions.

2. A higher vehicle test mass.

3. A lower engine temperature at test start.

The relative impacts of the three different regulatory issues are connected multiplicatively, adding up to a total of a 5.7% impact if a temperature correction is not taken into account (i.e., if the test temperature remains at 23 °C) and 7.7% if the test temperature is lowered to 14 °C. These estimates are based on the expected technology fleet mix in the EU in 2020.

It should be noted that from a customers’ perspective, the effect of the transition from NEDC to WLTP will likely be higher than expressed by the estimate above. This is because manufacturers today, to some extent, make use of the additional flexibilities provided in the NEDC regulation. Even though this is not illegal, strictly speaking, it contradicts the intentions of the original NEDC regulations. When switching from NEDC to WLTP, which limits these flexibilities and closes “loopholes” in the NEDC procedure, CO₂ emission values will become more representative of real-world driving and customers will benefit from these improved values. It is not the intention of the regulator to reward manufacturers for making use of unintended NEDC flexibilities, which is why it would be inappropriate to take this effect into account for determining the NEDC-WLTP conversion factor.

—Mock et al.

Implementing the WLTP. Manufacturers will need sufficient lead time to adapt to the new testing conditions, the report said. The authors recommended that testing continue to use the NEDC until 2017, allowing the 2015 CO₂ target of 130 g/km to remain unchanged.

The ICCT authors then suggested that the next step would be to add the WLTP for type-approval testing of new vehicles in 2017, such that new vehicles would be tested both in NEDC and WLTP. The legally binding values for the CO₂ monitoring would remain the NEDC results.

At the same time, the WLTP test results would be the basis for customer information (sales brochures and c02 labelling) and eventually national tax regulations, thereby creating a strong incentive for manufacturers to optimize their vehicles for the WLTP.

This would allow regulators and manufacturers to collect more experience with the effects of the WLTP and to prepare for the full switch to WLTP without revising the binding CO2 target of 130 g/km for 2015-2019. Given that this target was already met on average in 2013, it seems highly unlikely that any manufacturer will not meet it in the 2015-2019 time range, be it in NEDC or WLTP testing conditions. Therefore, translating this target from NEDC in WLTP for the 2015-2019 time range does not seem necessary.

From 2020 on, new vehicles would be tested in the WLTP only, and CO₂ emission targets would have to be met in the WLTP. For this, it is necessary to translate the existing 95 g/km NEDC-based target into an equivalent WLTP-based target. As shown in Section 3 of this paper, the resulting WLTP-based target value for the fleet average is estimated to be 100 g/km (without temperature correction). The EU CO₂ regulation includes a one-year phase-in period, requiring that only 95% of new car sales in 2020 comply with the CO target, that ss, the 5% of vehicles with highest CO₂ emission levels CO₂ emissions will not be counted in 2020 when determining whether a manufacturer met its target or not. This flexibility, together with the 2017-2019 double-testing period, and also the time frame between adoption of the EU-WLTP and its introduction for type-approval in 2017 will allow manufacturers a six-year lead time before fully switching to WLTP from 2021 on.

—Mock et al.

Resources

• Peter Mock, Jörg Kühlwein, Uwe Tietge, Vicente Franco, Anup Bandivadekar, John German (2014) “The WLTP: How a new test procedure for cars will affect fuel consumption values in the EU” (Working Paper 2014-9)