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From NEDC to WLTP – The impact of new economy testing procedures

BMW 330e

BMW 330e

Last year’s dieselgate scandal, in which Volkswagen admitted cheating during official emissions tests, has put the efficiency claims of all carmakers in the spotlight. It has also drawn attention to the inadequate state of official testing procedures in Europe.

While VW’s deliberate use of circumvention devices was particularly shocking, it exposed a system with much more widespread shortcomings. These include the apparently legal tactics employed by Vauxhall-Opel, Renault and Nissan of switching off emissions-reduction systems whenever outside temperatures fall below 17°C, as they do for the vast majority of the time in the UK.

Happily, Europe’s testing procedures are about to be toughened up. The feeble NEDC test (the inappropriately named New European Driving Cycle) will be replaced from September 2017 with the Worldwide Harmonised Light Vehicle Test Procedure (WLTP), which will rely on a new test cycle, WLTC.

At 30 minutes in duration, WLTC lasts 10 minutes longer than NEDC, leaves the car stationary for much less of that time, employs higher top speeds and requires faster acceleration. It still, however, leaves a lot to be desired.

“It will be an improvement on NEDC because it could hardly be worse, but it’s not going to be that much better and it’s not going to solve the underlying problem,” says Nick Molden, founder and chief executive of Emissions Analytics (EA), which has tested on-road emissions of thousands of vehicles using mobile measuring equipment. “To give you an idea, currently real-world CO2 emissions are about 39% above the official levels, on average. We think the introduction of WLTC will about halve that gap.”

The large differences measured by Molden’s company are corroborated by a study published in September 2015 by consultants Element Energy and the International Council on Clean Transportation (ICCT). Using two independent methods to assess real-world CO2 output, the report estimated that the gulf between NEDC figures and reality stood at 35% in 2014, having risen from 10% in 2002, and was on course to reach 50% by 2020.

The report predicted that the introduction of WLTP testing will reduce the divergence to 23% next year, with the gap rising once more to 31% by 2020 as manufacturers learn how to optimise vehicles to perform well under the new testing regime.

The outgoing NEDC has become infamous for allowing manufacturers to inflate the performance of cars by exploiting grey areas and loopholes. For example, the actual NEDC test is carried on a rolling road in a laboratory, without the car actually travelling anywhere. As a result, each test vehicle first needs to have its road friction and aerodynamic drag measured so that these can be factored in during the test. A report published in September 2015 by Brussels-based lobby group Transport & Environment notes that manufacturers typically prepare vehicles by adjusting the brakes, altering wheel alignment and even taping over parts of the bodywork to reduce friction and drag, thus making the subsequent test cycle easier on the engine.

Similarly, manufacturers can improve results during the rolling-road phase of testing through further tweaks, such as pre-charging the battery to reduce the strain on the engine from the car’s electrical system.

Phil Stones, chief powertrains engineer at vehicle testing services provider Millbrook, says many tales of rule-bending are not true, but concedes that manufacturers do tend to tend to push to the limits of the regulations. He adds that official tests are witnessed and settings are checked by the VCA, the responsible authority in the UK, but that inspectors can only enforce the letter of the law.

“The WLTP does get rid of some ambiguities in some areas,” Stones says. “For conventional vehicles you’re not allowed to put the battery on charge any more. NEDC regulations don’t say anything to prevent it, so therefore it’s open and you can put the battery on charge, whereas the new regulations stipulate that you can’t.”

Greg Archer, director of clean vehicles at Transport & Environment, agrees that many of today’s more pliable rules will be straightened out by the new procedure. “There are some additional loopholes that come in with WLTP,” he cautions. “For example, a number of cars are fitted with eco modes, so you can flick a switch and supposedly get better fuel economy. Will the car be tested in eco mode and the majority of people drive it in a different mode, for example? There are also some big questions around gearshift strategies in WLTP for manual transmissions, where manufacturers are shifting early to keep revs down and get good fuel economy.”

EA’s Molden also notes that WLTP remains a weak hurdle compared to the equivalent tests carried out by the US Environmental Protection Agency (EPA).

“They had the same problem we have in Europe about 10 years ago,” Molden says. “Their response was to add in extra cycles: high speed, cold start and air conditioning use. And those brought the average of their laboratory figures into line with the real world.” By contrast the incoming European testing process still does not factor in the potentially large impact of outside temperature.

Europe’s new tests are also unlikely to provide reliable data for plug-in hybrid vehicles (PHEVs). By their nature, these cars are hard to assess in official tests because the individual pattern of usage has such a bearing on fuel economy. If most of a plug-in car’s mileage is done on electricity, it will of course achieve very clean emissions and excellent economy results. But if it is only rarely plugged in, the situation will be very different.

WLTP figures will adopt the assumption that a plug-in car is driven on its battery for 70% of the time, says Archer. “But that certainly isn’t what’s being achieved at the present time,” he argues, quoting figures collected in the Netherlands that show plug-in hybrids run on battery only about 35% of the time.

Molden adds that the issue is particularly acute where PHEVs are chosen as company cars due to their favourable Benefit-in-Kind taxation rate. “If the company covers an employee’s petrol costs, whereas they have to pay for any electricity used on their home bill, they just let the company keep paying for the petrol,” he observes. “It’s a wrinkle in the system. If you have fuel paid for by your employer, you are incentivised to buy one of these things and then positively incentivised never to charge it up.”

Archer agrees: “One of the things we’ve been saying, particularly for company cars, is there ought to be some measure of the tax in proportion to how much it’s being driven in its electric mode. You could do that for a company car – you can require companies to compile quite detailed information, or you could have on-board metering.”

These and many other arguments remain to be resolved. Among them are how to communicate the changeover to the public, particularly given that there will be a period of transition between September 2017 and December 2019 when NEDC results will continue to be quoted for existing models while newly launched cars must be labelled using the tougher WLTP figures.

Molden also notes that the government is “working frantically” on the tax implications of the new test’s generally higher CO2 ratings. Given that the same car will produce different CO2 figures under NEDC and WLTP, the new test’s impact on road tax and company car tax has yet to be made clear.

“They could just leave the tax bandings as they are,” Molden observes. “You can imagine that the government might do that. Over the last five years or so the tax take has been falling, because cars have been moving into lower and lower bands. So they might use this to reverse that trend.”

By Lem Bingley

Read more about the NEDC test