This 2015 update to a series begun in 2013 analyzes eleven data sources covering fourteen years, six countries, and almost 600,000 vehicles. The analysis shows that in the EU the gap between official vehicle CO 2 emissions and real-world CO 2 emissions continues to grow—from 8 percent in 2001 to 38 percent in 2014.

Since 2001 average type-approval CO 2 emission values of new European passenger cars have decreased by 27 percent. The rate of decline quadrupled after the EU introduced CO 2 emission standards in 2009.

But the official vehicle CO 2 emission values are determined by laboratory tests. As previous "From Laboratory to Road" reports, published in 2013 and 2014, showed, there is a gap between the real-world and official CO 2 values that has been increasing over time.

For an average consumer the gap now translates into additional fuel expenses on the order of €450 per year. Since vehicle-taxation schemes and incentive schemes for low-carbon cars are based on official CO 2 values, the gap may also lead to significant losses of tax revenue and a misallocation of public funds.

This update identifes a number of reasons for the increasing gap. Flexibilities in the type-approval procedure allow for unrealistically low driving resistances and unrepresentative conditions during laboratory testing (these flexibilities account for the majority of the gap in 2014). Fuel-saving technologies such as stop-start systems and hybrid powertrains also prove more effective at reducing CO 2 emissions during laboratory testing than during real-world driving. Lastly, the type-approval process fails to take into consideration auxiliary devices such as air conditioning and entertainment systems. These devices consume energy during real-world driving and thus contribute to the gap.

The key implication of the study is the urgent need for improved test procedures. While a new type-approval procedure, the Worldwide Harmonized Light Vehicle Test Procedure (WLTP), will be introduced in the EU in 2017, the WLTP will not close the gap on its own. On-road tests, similar to the Real-Driving Emissions (RDE) test procedure for air pollutants, and in-use conformity tests of randomly selected production vehicles should also be introduced.