A new real-world test for diesel vehicles will begin today, to more accurately measure emissions of vehicles sold in the UK.

Starting from 1 September, tested cars will be driven on urban and rural roads as well as motorways, with measuring equipment placed on their exhaust system.

The evaluation, which replaces current lab-based tests, will last 90 minutes and focus on cars due to reach market in the UK in the coming months. From 1 September 2019, all existing cars on sale will also be retested with this new system.

Government estimates suggest the stricter tests, rolled out as part of European-wide reforms following the Volkswagen dieselgate scandal, will help to cut nitrogen oxide emissions from new diesel vehicles by two-thirds.

The Government claims that this reduction will be possible because where some cars were shown to have performed better in the lab than in real life, now they will have to conform to emissions limits in public - something that will force manufacturers to produce even cleaner powertrains. A diesel-testing programme last year found that several Euro 6 diesel cars were emitting around six times more nitrogen dioxide in the real world than in the lab.

Certain models, such as those caught up in Dieselgate, were engineered to perform better in lab conditions, therefore deliberately skewing their CO2 and NOx outputs in order to be categorised as lower-emitting vehicles. Others saw rises in emissions after 20 minutes – the duration of the lab test process. 

UK Transport Minister Paul Maynard said the new testing structure came as part of broader ambitions to improve air quality in Britain. From 2020, councils will be given power to enforce tougher restrictions on the highest polluters of nitrogen oxide.

“We are taking strong action to clean up our air and these tough new emissions standards will reduce dangerous pollutants,” he said. “This will ensure all vehicles meet rigorous standards when driven on our roads – and we are going even further by tightening requirements again in 2020.”

Earlier this year, the UK Government revealed plans to ban the sale of pure combustion engine cars from 2040. Some critics, including Aston Martin CEO Andy Palmer, believe the legislation will have little impact, because the market is naturally heading in this direction.

Also read: New WLTP and RDE fuel economy and emissions tests explained