A report from a body set up by the UK government to investigate climate change issues and policy has said that new EU CO2 emission tests for cars will fail to solve the problem of official figures showing large discrepancies with real-world results. Car manufacturers, it is suggested, will continue to work within testing rules to achieve results that are out of kilter with real-world driving experience.

The car industry has been accused of 'fixing' the official measures of fuel consumption testing – while working within the rules – by adapting tyres and taking weight out of vehicles testing (eg stripping car stereo and spare tyres) beyond what might be considered 'normal'.

The EU wants to introduce a tougher test regime by 2017, known as the worldwide harmonised light vehicles test procedure (WLTP), which supposedly is closer to real-world driving and closes 'loopholes' under the present NEDC test.

However, the new study commissioned by the UK Committee on Climate Change (CCC) suggests that some loopholes will remain alongside continued, if smaller, real-world discrepancies.

The CCC says that between 2002 and 2014, the gap between official and real-world CO2 emissions for new passenger cars increased from around 10% to about 35%. Most of this growth in the gap is due to increased exploitation of ‘flexibilities’ in lab testing (for example, by minimising the weight and rolling resistance of the vehicles being tested or optimising the environmental conditions in the laboratory), CCC maintains.

The anticipated introduction of the WLTP in 2017 is expected to reduce the gap for new cars to about 23% (from 35%) the report forecasts. “This is because aspects like vehicle test weight, test temperature and test driving pattern are estimated to be more in line with real-world driving for WLTP than it is currently the case in NEDC,” the report suggests.

Beyond 2020, CCC says the emissions gap could grow again to about 31%, even under WLTP, driven by possibilities for vehicle manufacturers to “exploit shortcomings of the new test procedure”.

Download and read the full report