Study: One-Third of “Green” Gains in Europe Due to Test Variations

European carmakers lowered the average carbon dioxide emissions of their cars 16% to 167 g/km between 2002 and 2010, according to the region's mandated testing method.

But a new study for the European Commission estimates one-third of the improvement came from "flexibilities" in the test procedure rather than real gains, Reuters reports.

Critics have pointed out for years that the European test procedure generates optimistic fuel economy ratings that are rarely matched by real-life driving conditions.

The study cites such loopholes as being able to run the test on an unrealistically smooth road surface that cuts rolling friction, thereby enhancing fuel economy and reducing CO₂. The resulting gap between claimed and real-world fuel economy costs each European driver as much as $180 per year in higher-than-expected fuel bills, according to the analysis.

The report was conducted for the EC by the Netherlands Organization for Applied Scientific Research, AEA Ricardo and IHS Global Insight.

Reuters notes that the EC expects to revise Europe's testing law by about 2016. The commission has cautioned that the update will reduce but not eliminate variability in the procedure.