It first came into force for new types of cars in 2017, but now the second stage of a three-part transition phase is here. From September 2018, the tests that have been used to assess the pollutants produced by cars and vans since the 1980s are to be replaced by a new set of standards for all new car registrations.
The new tests are known as the Worldwide Harmonised Light Vehicle Test Procedure (WLTP). The third and final stage of the transition will happen in September 2019, when the sales timeframe for a limited number of end-of-series vehicles approved under the old tests is due to end.
Also new for September 2018 is the Real Driving Emissions (RDE) test. This will work in partnership with the WLTP, and is designed to measure the pollutants cars emit when driven on real roads, as opposed to when they are tested in a lab.
The old series of tests, called the New European Driving Cycle (NEDC), has faced criticism for being outdated for some time so, as the new tests are much stricter, they should help to ensure more fuel efficient, less polluting vehicles on our roads in years to come.
You may already be aware that the WLTP has already impacted the limits of exhaust fumes that Diesel Particulate Filters (DPFs) allow into the atmosphere from diesel cars. This is something that has already become part of the latest MOT test.
What exactly is the WLTP?
The WLTP has been designed to measure the performance of cars in a lab against a set of target criteria, including CO2 emissions and fuel/energy consumption. It will ensure that a car manufacturer's new models do not emit more CO2 on average than EU targets.
Unlike the NEDC, which was based on hypothetical driving benchmarks, the WLTP is based on real driving data collected over many years from all around the world. Therefore, it should be much more representative of actual driving standards on today's roads, and the results should be much more accurate in terms of what you can expect from the cars tested.
How will the WLTP improve on the NEDC?
These are the main differences between the old NEDC and the new WLTP.
What will WLTP results tell me about a car?
The purpose of the WLTP is to make it easier to compare the fuel economy and environmental impact of different cars.
However, it won't reveal the miles per gallon (mpg) you can expect to get from one car to the next. Mpg depends on many different factors, such as traffic, the use of internal vehicle controls and even how many people are in the car.
As well as the CO2 emission levels we already see on car specifications, every model of new petrol, diesel or hybrid car introduced to the market will eventually have its own set of WLTP results. These will be recorded over four different sets of driving conditions - city (maximum 35mph), town (maximum 50mph), rural (maximum 60mph) and motorway (maximum 81mph) - as well as an average and overall fuel economy figure.
As the WLTP is much more stringent than the NEDC, it may seem as though many new cars are suddenly far less fuel efficient and more polluting, almost overnight. The levels will of course be the same as they were before, but stricter guidelines should encourage car manufacturers to make improvements moving forward.
Will the WLTP mean that I could end up paying more car tax?
For cars registered during or after March 2001, the amount of car tax payable is decided by the levels of CO2 they emit. In April 2017, new car tax rules were introduced that means anyone buying a new car must also pay an up-front CO2 emissions charge, based on how efficient their new car is.
The WLTP will likely result in many new cars suddenly recording much higher levels of CO2 emissions, simply because the new tests are more stringent, which could - in theory - mean much higher rates of car tax. However, there are no plans at present for car tax to be calculated on WLTP results; cars will continue to be taxed on their NEDC ratings.
Having said that, buying a new used car is a great way to avoid any forthcoming changes to the law relating to the taxation of new cars. As the introduction of the WLTP shows, new cars are often subject to new legislation, so opting for a used car can give you all the advantages of a top-quality vehicle without the additional financial burden.