Diesel or gasoline cars – which are better for the environment?

The US investigation into emissions from diesel cars has drawn attention to the difference between emissions performance during tests and real world driving. And despite recent allegations of attempts to 'cheat' US pollution tests by means of so-called 'defeat devices', the difference between 'normal or static' test data and on- road emissions is a different issue. Vehicle manufacturers and governments are well aware of the latter and have published research on this since at least 2011.

Nevertheless, the attention to both topics has opened up an old question – which is better for the environment, diesel or gasoline?