The current ‘Dieselgate’ scandal involving Volkswagen cheating on a US emissions test has caused a great deal of controversy.  People at Volkswagen have fallen on their swords, the share value has plummeted and it still remains to be seen how badly the company’s sales will be affected in the coming months.

It has also opened other cans of worms when it comes to the whole issue of how cars are tested for fuel consumption and exhaust emissions, and whether diesel cars should be taxed/banned/scrapped (depending on which lobby group you choose to align with) because we are now convinced they are killing everybody.

The issues have all become blurred.  On the one hand, Volkswagen is in trouble for cheating on a test because they were unable to pass it legitimately; on the other hand, people are complaining that testing is too easy and does not reflect ‘real-world’ driving. Diesel cars are now cleaner than they have ever been, yet there are growing calls for them to be banned from built-up areas. So let’s try and look at each issue separately.

The Volkswagen ‘Dieselgate’ issue

The Volkswagen Dieselgate scandal concerns the company manipulating its engines to deactivate emissions equipment in normal driving circumstances, meaning the affected cars are producing much higher levels of pollution than they should be.

A huge amount has been written already about Volkswagen’s specific case. A lot of it has been complete rubbish, some of it has been good and plenty is still speculation because there is still a long way to go before it is all resolved.

Read more Volkswagen news and reviews at The Car Expert

It’s fair to say that the company has done a Bad Thing, and it is going to cost them dearly in terms of fines and other penalties, plus the costs of ‘fixing’ the cars in question, plus the inevitable loss of sales and company goodwill, plus the hit to the company’s share price that has already led to the announcement that all non-core projects will be cut. This will not only affect the Volkswagen brand, but the other brands they own or control – Audi, Bentley, Bugatti, Ducati, Lamborghini, MAN trucks & buses, Porsche, Scania trucks & buses, SEAT and Skoda.
Volkswagen VW diesel TDI BlueMotion EA189 scandal 5

And of course, that’s assuming that authorities around the world don’t uncover any further cheating from Volkswagen as they now go about re-testing a number of vehicles. Things could possibly get even worse for the German giant…

Diesel cars and air quality

Any vehicle powered by an internal combustion engine produces some form of pollution. Carbon dioxide (CO2), carbon monoxide (CO), nitrogen oxides (NOx) and various other nasties all come out of engines – they always have done and they always will do. Modern engines are much more efficient than older ones, so they produce fewer pollutants, but they still pollute. Different engines produce different types and quantities of these gases, and this is where science and politics took us down a path that has proved problematic.

With increasing concern at the impact of CO2 on our planet and its contribution to global climate change, governments around the world started to introduce tough new CO2 limits for car manufacturers. As a result of this focus on CO2 emissions, in conjunction with rising oil costs, car manufacturers started investing heavily in developing diesel engines.

Diesel engines generally use less fuel and produce less CO2 than petrol engines. This is a good thing for global CO2 levels and the driver’s wallet, but the catch is that diesel engines produce higher levels of toxins like NOx. And that has become a problem.

NOx is a big local pollutant, which has serious health implications for anyone exposed to high levels of it for prolonged periods. The massive increase in diesel vehicles in built-up urban centres has meant correspondingly large increases in NOx being inhaled by everybody, and scientists are now suggesting that this is having serious effects on our health. Hence there are growing calls for diesels to removed from urban centres, one way or another. Manufacturers and their representatives are terrified at this prospect, since they have invested billions of pounds in current and future diesel cars, and they stand to lose a lot if there is a move away from diesel cars.

CO2 is still a big global problem, but NOx is a big local problem. CO2 won’t kill you now, but NOx will. However, CO2 could kill all of us eventually. Chasing CO2 – and therefore pushing diesel engines – at the expense of everything else for the last decade was the wrong move, but a kneejerk change of policy could create even more problems in years ahead.

We need to balance the two. In an ideal world, diesel would be limited to motorway and A-road vehicles, and petrol would be limited to city driving. But we don’t live in an ideal world and we need solutions that are realistic.

Also, it is a ridiculous situation that buses, vans and taxis have been exempt from the tougher emissions laws applied to passenger cars over the last years. These make up a huge percentage of the vehicles on city streets each and every day, and they produce far more pollution than any Volkswagen…

A typical London black cab produces far higher levels of emissions than a passenger car

Testing cars for fuel consumption and emissions

All manufacturers use various methods to ‘optimise’ their cars’ performance in lab testing environments. These methods are perfectly legal, but they do distort the laboratory results compared to normal driving circumstances.

We have written previously about the variation between lab tests and ‘real-world’ conditions, and debate has now been ignited about how cars should be tested for emissions and fuel consumption. After years of building discontent, the Volkswagen Scandal has triggered a real push from various quarters to see the rules updated.

The idea that official fuel consumption and emissions testing should be done in the ‘real world’ sounds great in theory, but wouldn’t work at all. How can you compare Car A tested by Team B on Test Route C in the UK, with Car X tested by Team Y on Test Route Z in another country? The variations would be enormous. Lab testing allows us to eliminate the variables, so everyone is measuring the same thing in a comparable fashion. What we need is for the lab testing to be far tougher, so it is representative of the load that engines face in normal driving.

emissions test on a Volkswagen Golf TDI


EVs and alternative fuels will have to play a much bigger role if we want to keep reducing CO2 while also controlling NOx and other local pollutants. Ultimately, we need to reduce our reliance on fossil fuels (if we stopped buying oil from the Middle East and relied on our own reserves, there’d be far less violence in the Middle East for a start, but that’s another story…).

The future of the car will not be straight choice between petrol and diesel. We need to make sure both are being used in the most favourable circumstances, and push ahead with other energy sources like natural gas and biofuels. We will also see more vehicles where a petrol/diesel/natural gas/hydrogen engine is used to generate electricity for an electric motor to do the actual driving. Electric motors are far more efficient than combustion engines, and this is where the big future lies.Diesel car exhaust producing emissions


  1. Volkswagen are deliberately dragging their feet in fixing these cars. Do they expect we will just forget about them if they take long enough to sort it? They should be made to take the cars off the road until they are fixed, that will teach them when their customers are screaming because they can't drive anywhere.

  2. The Volkswagen Audi Group (VAG) make high quality cars. I drive an 07 plate Skoda Fabia vRS which I have had from new. It is the best car I have ever had and it now has 180,000 miles on it. It is unfortunate that VAG have been caught out in this emissions scandal. I am sure that they are not the only ones. The problem is that unrealistic targets have been dreamed up which is the reason why this situation has happened. As an engineer I believe that the future of cars and larger vehicles will be in diesel/electric technology. Motorcycles will be best with petrol as a diesel engine would cause a significant weight gain. Modern engines also need to be made more able to run on biofuels without causing them damage.

    • vw haven’t been ‘caught out’ in ‘this emissions scandal’, they ARE this emissions scandal.
      i was personally about to buy a diesel car, however now with this matter coming to light i feel i would be very foolish to do so, no one has any idea where diesel is going in the future, let alone IF it has a future.

  3. (Modern engines also need to be made more able to run on biofuels), so you starve the poor to run your car, CO2 is not a pollutant it`s a plant food, no CO2, no plants, no oxygen.
    The most accurate temperature measurements taken from Satellites show the planet has not warmed for almost 20 years while CO2 has increased substantially over that time and the planet has greened because of the extra CO2.

    Make CO2 a pollutant and tax the air you breath.

    • I think you must have been reading a different article, because there is nothing in this one that remotely denies the effect of humans on the planet’s climate…

      • That’s all we need… Yet another moron posting comments before fully reading the article.

  4. I’m curious why you recommend diesel for the country (petrol in the city) in an ideal world.. Does the Nox dissipate more readily in country driving (whereas CO2 accumulates, becoming the global problem you mention?)

    • Hi Jim. Burning a litre of diesel will always produce a similar amount of CO2 and NOx, regardless of where you do it. However, a diesel car is very efficient in steady-state driving and is therefore burning very few litres. In city driving, with a lot more accelerating and braking and idling, it burns far more litres.
      In addition, the confined spaces of urban areas work to keep the pollution more contained, creating a build-up of pollutants which take longer to dissipate – hence the health concerns. Cities like Beijing have days where all cars are banned, simply to allow the pollutants to disperse.

      • Hi Stuart, I see what you are saying about urban areas and build-up of pollutants – interesting about Beijing banning cars on some days. I think you are also saying that Diesel engine economy drops proportionally more to petrol (& likewise CO2/ NOX emissions increase) in urban driving. I hadn’t realised that – as well as the recent concerns about diesels emitting more than the official figures, it belies the idea that diesel = more efficient, for many drivers.

        Personally, I’m looking for a new car to commute/ drop off kids in town – so a mixture of town/ country/ dual carriageway + a fair few miles each day. Wouldn’t one of those fuel cost calculators, but with an emissions estimation on top, be great here?

  5. Something that everyone misses is that petrol catches fire much more easily than diesel. That is why nearly all boats use diesel, no fire brigade at hand ! Petrol vehicles catch fire VERY easily if the preventative systems are not working. Furthermore diesel engines do not require electricity to keep them running. If petrol engines get wet they do not work, diesels do.

  6. Maybe in the 1980,s they don’t need electricity but a modern diesel has an ecu ,electronic sensors all over the place.please get with the times

  7. Will the introduction of adblue to new diesels be given any consideration regarding increased tax on diesel cars or will all diesels be lumped together?

    • Hi Rog. Different penalty charges and taxes will be applied differently. The proposed ULEV emissions zone for London will only penalise older diesel cars, so the latest Euro-6 engines (which are the ones which may use AdBlue) will not be affected. Other charges may apply differently in the future.
      Currently, road tax is worked out based on CO2 emissions, and even under the new road tax rules this will still be the same.
      Looking ahead, it seems likely that all diesel cars will eventually be penalised more harshly than they are today, but it’s also likely that the charges for petrol cars will also increase.

  8. Petrol cars emit 10 times more hydrocarbons, carbon monoxide,30%more co2,and let’s not forget benzene that we’ll known carcenognic lead,chromium.and if you own a Gdi petrol car direct injection they emit 10 times more particulates than diesel (fact).

    • Will G Durant please post the relevant stoichiometric combustion calcs for perusal, to support his claim. Naturally the complete balanced chemical reactions for each fuel type are required to do so. It is also directly proportional to the QUANTITY of each type of fuel combusted in each vehicle, which is directly proportional to the engine capacity & RPM. To do this fairly you would have to consider a few popular vehicles, so it’s quite a big exercise. It would be unfair to compare e.g. a 1.4 diesel to an 8 litre Vortex petrol V8 as found in the Chev Suburban (though the engine cuts to 4 cyls at low power economy mode)

  9. I think that diesel vehicles should be work vehicles like they used to be before Labour conned us in to bye diesel vehicles because they found a cheap supply of diesel which resulted in more revenue for a wasteful Labour government , its ok to tell us to stop using these vehicles but what alternative is there for a working vehicle as you need low down power of the diesel engine to pull weight

  10. Shame that it beyond the wit of man to be able to filter out these particles and/or in part ‘deactivate’ the (NOx). Note for ‘Mr Angry’ – chemistry not my strong point…just a comment!!

What are your thoughts? Let us know below.