1.What is the relationship between the official VCA fuel consumption figures (based on a rolling road) and the Honest John figures (based on ‘real world’ driving)?
Comment on the nature and strength of this relationship, and the implications for this research.
2.How big are the differences between the VCA figures and the Honest John figures?
What is your estimate the average difference for all cars in the UK, for each fuel type?
3.Does the fuel type of the car seem to influence the size of the differences?
Are petrol and diesel cars significantly different in this respect?
4.Does the ‘size’ of the car seem to influence the size of the differences?
In other words, is there any evidence that the rolling road appears to favour smaller cars, compared to larger cars, as suggested/suspected on the previous page?
5.What is the relationship between fuel consumption (either MPG or LpKM) and CO2emissions?
Hence, is fuel consumption a reliable indicator of CO2 emissions for a vehicle?
Do petrol and diesel cars differ in this regard?
6.The current DBEIS model uses VCA-based CO2values for a range of cars to estimate total CO2 emissions for the whole of the UK (see spreadsheet).
Based on the findings above – in particular any relationships found in task 5 – how might we sensibly uplift the emissions predictions to produce a more accurate ‘real world’ estimate of total UK CO2, as we suspect the VCA-based CO2 values are too low?
Do your results support the idea of a suggested uplift of 10%?
The present analysis seeks to investigate the differences in estimates of fuel consumption between the vehicle certification agency (VCA) and honest John (HJ) figures. The analysis was done using the data set 2017 Data for group 13. The data set contains the fuel consumption of 100 petrol and diesel vehicles. The data also contains information on CO2 emissions of the vehicles. The rationale for the analysis is to compare the fuel consumption and CO2 emissions of the vehicles. The inference from the analysis is used to estimate the CO2 emissions in UK. The presumption of CO2 emission is compared to propose if the VCA recommended values need revision.
1.There is a very strong, positive relationship between the official VCA fuel consumption figure and Honest John Figures. The correlation between the two figures is r = 0.89.
Figure 1: Relation between VCA and HJ Figures.
1.According to HJ the minimum and maximum mileage of the vehicles are 26.17 and 67.42 miles per gallon respectively. On the other hand according to VCA the minimum and maximum mileage of the vehicles are 28.5 and 80.7 miles per gallon. The average fuel efficiency of the vehicles according to HJ (46.55± 8.38) is less than that of VCA (53.81± 11.09).
The 95% efficiency of the vehicles according to HJ is less than efficiency of VCA.
Figure 2: Differences between VCA and HJ
Figure 3: Difference between VCA and HJ on the basis of fuel
Comparison of the mileage according to the type of fuel shows that the minimum mileage for diesel and petrol are 41.5 and 28.5 miles respectively. Similarly the maximum mileage for diesel and petrol are 80.7 and 68.9 respectively. Likewise the comparisons also show that the minimum and maximum mileage for diesel is more than that of petrol. In the same way the analysis of the data shows that the average for diesel (60.08 miles per gallon) is more than that of petrol (47.55 miles per gallon) according to VCA data. The data for HJ also shows similar results.
4.To analyse if the rolling road favours small cars the data of the cars were divided into two groups. The small cars consisted of Lower Medium, Mini and Super mini vehicles. The large cars consisted of Large Car, MPV, SUV and Upper Medium vehicles. The analysis of the data shows that there is no difference in fuel consumption when comparing small and large vehicles.
Figure 4: Relation of mileage and CO2 emissions of all vehicles
There is a very strong negative relation between mileage of a vehicle and CO2 emissions. With increase in mileage of the vehicles there is a decrease in CO2 emissions of the vehicle.
Figure 5: Relation of mileage and CO2 emissions of petrol and diesel vehicles
The relation between mileage and CO2 of both diesel and petrol vehicles show a similar trend. For both types of vehicles with increase in mileage of the vehicles there is a decrease in CO2 emissions. However the relation among mileage and CO2 for diesel vehicles is stronger as compared to petrol vehicles according to the data provided by VCA.
6.The amount of variability in CO2 emissions which can be predicted with VCA data is higher for all types of vehicles as compared to HJ figures. For petrol and diesel vehicles with the help of VCA data 96.7% and 93.2% of CO2 emissions can be predicted from the fuel consumptions of the vehicles. Similarly 84.2% of CO2 emissions can be predicted for all vehicle types from the fuel efficiency data provided by VCA. This is higher than the level of predictions that can be done with HJ figures.
Thus it can be said that VCA figures are highly realistic figures as compared to HJ figures. Hence we find that there is no necessity to uplift the emission data.
The analysis of the fuel consumption data shows that the fuel efficiency of both VCA and HJ provide similar results. The analysis shows that the measurements of minimum, maximum and average fuel efficiency according to HJ is lower than that of VCA. Similarly the 95% estimate of fuel efficiency of HJ is lower as compared to VCA. The analysis further shows that the fuel efficiency of Diesel vehicles is more as compared to petrol vehicles. Moreover the fuel consumption of petrol and diesel vehicles is similar. The emission of CO2 decreases with increase in fuel efficiency of the vehicles. The decrease in CO2 emission from diesel vehicles is less as compared to petrol vehicles. In addition the analysis of the data shows that the CO2 emission level as reported by VCA is higher th