Last reviewed 8 October 2015

Richard Smith, transport consultant, summarises the facts of the recent Volkswagen emissions scandal and looks at the wider implications for the transport industry.


Readers cannot have escaped noticing the recent Volkswagen emissions cheating scandal, though the media’s enthusiasm for reporting it has not always been matched by accuracy of technical knowledge. There is currently no evidence that large commercial and passenger carrying vehicles are affected in any way, although some smaller vans are: however, there are some important lessons to be learned.

What happened?

What is indisputable, because they have admitted it, is that VW programmed the engine management software for one of its range of engines with code that detected when the vehicle was being tested on a rolling road and switched the engine to a special operating mode that artificially reduced emissions of nitrogen oxides (NOx). It was able to do this (presumably through the ABS wheel sensor signals) because only one pair of wheels would be rotating.

It is likely that the cheat-mode would have obviously affected the performance if in operation on the road, but this would not have been noticeable within the relatively restricted conditions of the type approval test. Once on the road, the engines switched out of this cheat mode, giving normal performance but increased NOx. Only NOx emissions were concerned so on normal in-service testing under static conditions (such as during the MoT test) — where NOx emissions are not measured — the cheat would not have been noticed even though the special operating mode would not have been in operation.

Which vehicles are affected?

The engine in question is the type EA 189 EU5 4-cylinder diesel engine installed in various vehicles between 2009 and 2015. The total number of vehicles concerned is about 11 million worldwide but most of them are cars, badged not only as VW but also Audi, Seat and Skoda. However, some 1.8 million small commercial vehicles also have this engine, with nearly 80 000 of them in the UK.

What will happen now?

There will be no formal recall (through DVSA) because this does not affect roadworthiness, the Department for Transport has said that there is no obligation for owners to get the offending vehicles modified, and it would not be illegal if they were not. Vehicle Excise Duty is calculated on carbon dioxide emission so will there not be any effect on that either. Indeed, because the cheat was discovered in the USA, where emissions limits are much lower than in Europe, it is not yet clear whether the EA 189 engine — without the cheat-mode in operation — would exceed the Euro V limit for NOx.

Nonetheless, VW will contact owners of the affected vehicles (via DVSA) and offer a fix that is reported to involve fitting the Euro VI specification exhaust system that uses the selective catalytic reduction (SCR) with urea (AdBlue) injection that will already be familiar to operators of latest specification lorries and buses. The modification will be carried out free of charge but, it has been reported, will cost owners a whole £50 a year more on running costs thereafter to keep the AdBlue tank topped up. An alternative would be to embed the cheat-mode software as the normal running mode – a quicker and cheaper fix but with a detrimental effect on performance and increased fuel consumption.

Wider implications

This affair really highlights a number of issues that have been noted for some time: the discrepancy between type approval testing and real life, the foolishness of the “rush for diesel”, and a concern that the regulators have been attempting to push the boundaries too far, too quickly.

The rush for diesel

Initial concerns in connection with type approval emissions testing were over carbon monoxide and unburnt hydrocarbons, both of which were known to be harmful to humans and were the subject of the first EU emissions regulations in 1970. Limits for NOx were added in 1977. At this time, the overwhelming proportion of light vehicles were petrol driven and the three-way catalytic converter introduced in response to the 1991 regulations (Euro 1) effectively reduced all the above emissions to very low levels. The harmful nature of particulate matter, which is really only significant in diesel exhaust emissions, was also known and these were also regulated.

Then came the great global warming scare which implicated carbon dioxide (CO2) as the cause, despite science having taught previously that it was only the “greenhouse layer” of atmospheric carbon dioxide that made earth inhabitable. CO2 emissions were now also tested (but not regulated) and in the UK the Vehicle Excise Duty system was changed to favour cars with lower CO2 emissions. Because of their inherently greater efficiency diesel engines produce less CO2 than petrol-powered ones and the basis of VED was again changed in order to promote a switch to diesel fuel. This was against the recommendations of engineers who knew that there was a much greater threat from the particulates and NOx that diesel engines produce.

Certification testing

There has long been criticism that the fuel consumption figures obtained in the official EU test have not been achievable in real life, and we have now seen this extended to exhaust emissions. It was on-the-road testing by the US Environmental Protection Agency that revealed the VW cheat. In fact, we should not expect certification test figures to be achieved on the road for there are so many variables at play that it would almost amount to pure luck if they did.

Any certification test needs to have two key features.

  • It must be consistent, ie exactly the same conditions must apply every time the test is made.

  • The results must be repeatable, ie if the same vehicle is put through the same test twice the results must be broadly the same each time.

Therefore, because of the impossibility of ever achieving these two conditions on a real-life road test with a human driver, certification testing must be carried out on a rolling road using a standard test sequence controlled by computer. The required limits for emissions are set relative to this specified test procedure and there is no reason why there should be any correlation between the figures achieved on the certification test and those achieved on a road test — even when the road test is carried out on a traffic-free test track using the same test sequence, much less in general driving.

The same is true for fuel consumption figures, which the EU have never said should be representative of the absolute mpg achieved in practice but are only for the purposes of comparison between different makes and models.

Pushing the boundaries

Concern has also been expressed that the regulators are setting unrealisable goals for manufacturers by expecting ever-lower limits to be achieved within unrealistic time-scales and this has been the case ever since the Euro I limits were introduced. In 1991, a number of manufacturers were making good progress with lean-burn petrol engines that, in the longer term, would have produced much better fuel economy with much lower emissions of all combustion products — including CO2. However, the time-scale for entry into force of the Directive meant that this development could not be realised in time and the fitting of catalytic converters — which increase fuel consumption and CO2 emissions — was the only viable option. A similar situation has existed with subsequent iterations of the regulations.


While there can be no denying that VW did deliberately set out to break the rules, a principled analysis of the entire issue does reveal that unwise or hasty decisions by legislators has played a part. Manufacturers have been forced to adopt potentially dead-end technologies such as catalytic converters and particulate traps in the short term and have only been able to make real advances over the longer term. This may not be too important in the car market where economic life is quite short and prices relatively low, but with lorries and buses that are very expensive to buy and have long economic lives, environmentally-conscious operators will have been forced constantly to upgrade their fleets with stop-gap solutions.