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The current method of testing fuel economy and emissions has had its day. Condemned for its inability to reflect real-world mpg, the New European Driving Cycle (NEDC) will be replaced across Europe, including the UK, in September 2017 by the Worldwide harmonised Light vehicles Test Procedure (WLTP).
At first, the WLTP will only apply to newly introduced cars; existing models become subject to the regime in September 2018, and although no test can imitate everyone's right foot, the results are generally considered far more realistic, with numerous bodies suggesting a circa 50% increase in accuracy.
"There are still flexibilities, it's still lab conditions, but it does produce results that are more representative of real driving than the old test," said Dr Tim Barlow, technical manager for air quality and emissions at the Transport Research Laboratory (TRL).
What is concerning for fleets, is that stricter testing is expected to lead to greater official CO2 figures and therefore higher tax, but the new regime also removes some of the opportunities for manufacturers to fine-tune their vehicles to perform better in the test.
"The NEDC is full of loopholes that can be exploited," said Nick Molden, chief executive officer at Emissions Analytics. "You can overinflate tyres, the coast-down test [where neutral gear is engaged at a motorway speed and the vehicle is left to roll] can be manipulated in lots of ways, so you effectively get a better result. The new test will close a lot of those loopholes."
"Currently, you're allowed to put the battery on charge before the test," added Phil Stones, chief engineer for powertrain at vehicle testing facility Millbrook Proving Ground. "It isn't actually referenced in the regulations, so it's open at the minute, but in future you're not going to be able to. The vehicle will also be simulated part laden, so for a passenger vehicle it adds 15% payload and for an LCV it adds 28% payload."
Optional extras will also have an impact on CO2. Both a base and a top-spec vehicle will be tested respectively, while a calculation will be made to adjust the overall CO2 figure to incorporate any equipment that adds weight (e.g. air-conditioning) that could be specified in between the entry-level and top-end models.
Despite such efforts to tighten the rules, the WLTP test is still conducted in laboratory conditions and in a similar manner to the NEDC, although it does incorporate higher speeds: "Essentially, the process is very similar to the old one [but] it's a much more transient drive cycle," said Stones. "It goes up to 131kmh [81mph] where the NEDC only goes up to 120kmh [75mph]. [That means] the cycle is more dynamic and more like real driving."
The way in which fuel economy figures are presented will also change: "The old NEDC was a 20-minute, two-phase test [and it's] replaced by the World Light duty Test Cycle (WLTC), which is a 30-minute, four-phase test," added Stones.
"Currently, you get urban, extra-urban and combined fuel consumption figures; with the WLTC, you get low, medium, high and extra-high - and a combined figure as well."
According to Stones, this fourfold set of results will be presented in a different way, potentially in a similar fashion to alphabetical energy rating tables, usually used for white goods such as washing machines and fridges.
In spite of the new test, the NEDC's legacy is far from over and the motor industry will continue to depend on it beyond 2020, as Rob Gardner principal environmental consultant at TRL explained: "The [European Commission's] target is a 95g/km average fleet by 2021; that remains the same but it's based on the NEDC cycle. New vehicles will be produced to the WLTP regulations, so the CO2 results won't be directly comparable with the target.
"The Commission is having to create a new regulation, called the Correlation Regulation, which uses a special tool to show what [the figures] would have been under the NEDC. There's definitely some confusion because there will be two sets of results and I'm not sure how those are going to be communicated."
However, there are concerns that the WLTP doesn't go far enough: "On paper, the cycle looks more aggressive but because it's still in the laboratory, there are no hills involved," said Molden. "It's assuming completely flat ground, and although the car reaches higher speeds, the rates of acceleration are not much greater. Higher speeds can make a car more efficient too; about 50mph is probably the most fuel-efficient speed, and there will still be ways of manipulating the system."
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