1. Comparison NEDC/WLTC
Comparison of the influence of weighting factors as proposed by France on the validation 2 CO2 emission results for the WLTC
By H. Steven 1

2. Introduction
French authorities expressed doubts that the WLTC would represent the in-use driving behavior in France appropriately and proposed to apply weighting factors to the different phases of the WLTC in order to improve the situation.
The weighting factors that were proposed are 75% for the low and medium phases and 25% for the high and extra high phases.
This would lead to a 10 km/h lower average speed (36,5 km/h instead of 46,5 km/h) than the average speed of the WLTC.
In order to assess the influence on the CO2 emissions these weightings were applied on the validation 2 results. 2

3. Results
The calculations were performed per each individual test result of the validation 2 tests on all tests, where the full cycle was driven.
In a second step the results per vehicle were averaged for all tests, even if parameter variations were performed.
The direct comparison between the weighted and unweighted results is shown in figure 1.
Figure 2 shows the relative differences versus the unweighted results.
As one would expect, there is a high correlation between the results, but the differences are not correlated to the unweighted CO2 emissions. 3

4. Direct comparison of the results
Figure 1 4

5. Differences vs unweighted results
Figure 2 5

6. Results
And also the correlation with power to mass ratio is rather poor (see figure 3). In total less than 40% of the variation of the differences can be explained by the power to mass ratio.
In the meantime Fiat provided its ecodrive in-use database in order to support the French concerns.
The analysis of this data showed an average speed of 40,4 km/h, which is significantly higher than the French proposal but also significantly lower than the WLTC.
This average speed would lead to weighting factors of 65%/35% according to the French weighting approach. 6

7. Differences vs power to mass ratio
Figure 3 7

8. Results
The following figures ( figures 4 to 6) show the results, when these weightings are applied instead of 75%/25%.
The correlation between both results is, as expected, better than for the French weighting proposal. R² is 99% and the differences are not correlated to the unweighted CO2 emissions.
And also the correlation with power to mass ratio is equally poor as for the French weighting proposal. 8

9. Direct comparison of the results
Figure 4 9

10. Differences vs unweighted results
Figure 5 10

11. Differences vs power to mass ratio
Figure 6 11

12. Conclusions
To be added 12