Posted by & filed under CSAG student blog.

In 2010 the number of registered cars in the world hit the 1 billion (10⁹) mark (see Ward’s Auto, or, if you want to try some Dutch, Autoweek). This represents a major concern in climate change mitigation. While carbon taxes on private and company cars have been implemented in many places (including in SA), I will argue that the current approach is artificial and is not necessarily achieving what it has set out to do. Some relevant background can be found in my other blog on this topic.

The problems with current policies stem, in my opinion, from the consideration of tailpipe emissions only, the artificial nature of the test conducted to establish official figures for CO₂ emissions and the fact that driver behaviour is not taken into account. Also, how kilometre charging (a form of carbon taxing described here) would differ in its effects from fuel taxes, other than shielding industry (trucks need not pay kilometre charging, but are affected by fuel levies) and those who drive uneconomically, is not clear to me.

Certainly, a question that requires answering is what advantage these carbon taxes on motor vehicles have over simply increasing fuel duties. Here, a number of studies have been done, which have generally found a dramatic decrease in average vehicle fleet emissions since the introduction of these taxes; far more rapid than the slow decline that occurred between 1995 and 2005. In contrast, higher fuel taxes seem to encourage people to drive less, but doesn’t necessarily provide a strong enough incentive to buy a more economical new car. While this may indicate a trend towards people buying more economical cars (certainly, anecdotal evidence from European automotive fora indicates a strong tendency for new car buyers to want to select cars that are exempt from certain taxes or fall into lower company car brackets, for obvious financial reasons), one should be careful in ascribing all the decrease in fleet emissions to such policies. In particular, ambitious binding targets for CO₂ emissions, to be applied to each  car manufacturer (charges will be levied on companies that fail to comply) set by the European Union, to come into force this year, would certainly have pressurised manufacturers to improve the efficiency of their products.

As such, the number of cars on the European market that are now fitted with fuel saving devices such as start-stop (which automatically switches off the engine when one stops and then switches it back on when accelerator pressure is applied), brake energy regeneration and low resistance tyres,  has increased dramatically in the last three years or so. These changes almost certainly contribute to reduced emissions at a reasonable cost to the consumer (since much of the cost is implicitly carried by the state) and thus it appears these changes should be lauded (more cynically we may ask why we had to wait so long for them to be introduced in the first place).

Other changes have included the introduction of double clutch automatic gearboxes, semi-automatic and sequential transmissions, adaptations to gear ratios, tinkering with engine management and the introduction of electronic power steering. Above all, a trend has emerged that has become known as downsizing – smaller capacity engines, often are fitted with turbo- and/or superchargers, are replacing low stress, larger capacity engines. Here matters become more complicated: tuning and tinkering is generally done to gain advantage over competitors by reducing official emission figures just sufficiently to fall within a lower company car tax bracket, or below the tax-free threshold, in some key market. For example, a car officially emitting just 2g/km less than a primary rival could gain a massive competitive advantage in markets with a large leasing share (such as the UK or The Netherlands). Not only does this favour companies that already have large market share and can therefore afford to spend money on such tinkering, but it potentially also offsets resources that would otherwise have gone into the development of new generation engines with greater efficiency.

Even worse, perhaps, is that evidence from tests conducted by motoring journalists, as well as consumer reviews (see, for example,, suggest that there may be no significant real world advantages in many cases; sometimes, so-called green models in practise consume even more fuel than the cars upon which they are based. How can this be? Since manufacturers are well-aware of exactly how the official test to establish fuel consumption and emissions is conducted, they can adjust their engine management, gear ratios and so forth to these artificial conditions. Since the test is conducted under conditions that keep engine stress levels low and smaller force-fed engines increase their consumption far more rapidly at higher engine stresses, the test is substantially biased in favour of downsized engines. This would all be well and good if drivers could be forced to emulate the actions taken under the test conditions. However, apart from the meek efforts to encourage the inclusion of gear change indicators in modern vehicles, little has been done to alter individual driver behaviour, even though studies by the European Union have found that inefficient driving techniques (not including speeding!) can increase emissions by as much as 20% in extra-urban driving environments and as much as 40% in city traffic (approximately equivalent to advances made in engine efficiency over the past two decades!)

Another problem that has come to light with many of these new, supposedly more environmentally-friendly technologies, is reliability concerns. Problems with the distribution chains in the Volkswagen Group’s downsized TSi engines (fitted to models from Volkswagen, Audi, SEAT and other companies) have made headlines in Germany of late, whereas double clutch transmissions have also become notorious for their vulnerability. This leads me to probably the most glaring flaw in the current taxation system: it applies only to exhaust pipe emissions. The effective emissions from sources are simply not taken into account in legislation. These include: more complicated manufacturing processes; more advanced refineries needed to produce the much cleaner diesel required by modern diesel engines with their lower particulate emissions; electricity-intensive aluminium smelting (often done in countries like South Africa that produces cheap and dirty electricity) used to produce lighter parts to contribute to greater fuel efficiency; and especially from having to replace vulnerable parts and produce  more new cars to replace old ones that are scrapped because of high taxation levels or government subsidies. Some maverick studies have attempted to include all such variables and have produced extreme results, such as that a Jeep Wrangler is more environmentally-friendly than a Toyota Prius. However, the assumptions made by such studies should be treated with a healthy dose of suspicion, especially given the potential biases of the investigating agencies.

In terms of considering driver behaviour, my personal experience, in driving my dad’s car with a fuel consumption read out on the trip computer, is that being able to see immediately the effects of certain practises in increasing or decreasing consumption has a significant direct impact on my driving style, that is not achieved by watching the demoralising climb of fuel costs at the pump. Perhaps making such read-outs mandatory could begin to achieve what many more complicated measures have failed to realise.

Therefore, while the intention to reduce greenhouse gas emissions from road vehicles may be very noble, there seems to be no guarantee that current policies are actually achieving this goal. I would therefore suggest that to refine legislation, new studies are needed that take a more holistic, global approach to emission control and compare the consequences of rival policies.

4 Responses to “Automotive carbon taxes: help or hinderance?”

  1. Chris

    Actually a lot of modern engine management systems completely shut off the fuel supply when you take your foot off the throttle but stay in gear. On our golf TDI the fuel rate reading drops to zero when you do this so you can run down long hills burning absolutely no fuel. Older carburetor based engines almost did this but not as well. So I think these days its safe to say that staying in gear down hill is better for you fuel consumption though of course you will slow down faster…. One thing I will agree with is that having a continual readout of fuel consumption seriously changes your driving habits… for me its become a challenge on longer trips to see how low I can get the trip average!

  2. cbrodrick

    I’ve also heard that by utilizing engine-breaking on downhills, less fuel is used than by coasting. It may be partly due to the wheels driving the shaft which drives the pistons, therefore acting to assist the ignition/combustion stroke. As a result the engine is under far less stress and only has to use fuel to keep the engine running.

    I must admit that I’m not too geared-up on the functioning of hybrids, but I believe you are correct in saying that all mechanicals do not shut-down completely when the engine is ‘stopped’.

  3. Stefaan Conradie

    Thanks for the comment, Tiff.

    You might be interested to know that, in fact, using engine breaking and keeping revs higher on down hills uses LESS fuel than coasting. I could not believe this when at first I noticed it while driving my dad’s 406, but I’ve read up on it and an engine requires more fuel to keep running while disengaged from the wheels than when it is kept running by them. Therefore, engine breaking and staying in gear when approaching traffic lights, saves not only wear on the breaks and the clutch, but also fuel. As I said, this is the kind of interesting and potentially very useful information that can be gained from a fuel consumption read out.

    Similarly, accelerating hard from below about 1/3 of the maximum revs of an engine (~2000rpm for most petrol engines) not only increases wear, but also (when measured against distance, rather than time) actually generally increases consumption. The only time it is efficient to run at low revs is when you are applying little or no accelerator pressure.

    About start-stop I’m not sure, because the whole set-up of the alternator is changed and the drive shaft is kept running in neutral when the engine shuts out, as far as I understand, so I don’t know how much additional wear results from these systems. Also, all hybrids continuously switch the internal combustion engine on and off, as required, yet Priuses and Insights generally have strong reliability records (see JD Power or WhatCar? or similar surveys).

  4. cbrodrick

    I agree with you that the one-dimensional ‘tail-pipe’ emissions criterion is woefully inadequate, and you provide sound reasons why this is the case. Is it time for South Africa to implement strategies to remove vehicles older than a certain age (say, for example, 7 or 10 years) from our roads, such as Japan (and other countries) has done (are doing), on the principle that these vehicles are inefficient compared to modern standards? (for those of you wondering about classic cars etc. this does not apply to them).

    I share your sentiments that down-sizing engines is not all-together beneficial. Regardless of how technology has advanced, I believe that increased wear will occur on engines with stop-start technology, as each time the engine has to restart, the first revolution or two of the engine occurs without maximum oil volumes and spread over the moving parts. This may lead to reduced lifespan/increased servicing, which in turn has its own carbon footprint.

    The same applies to over-efficient driving. If the engine revs are kept too low, the potential exists for one to ‘lug’ the engine while accelerating, which is detrimental to the life of the engine. In order to save fuel, some drivers ‘coast’ on the downhills with excessive use of the brakes to reduce speed, thus a small amount of fuel might be saved at the the expense of the brake pads. Instead, engine braking should be applied: keeping engine revs higher allows the rotation of the driven wheels to be limited by engine load, thus negating appreciable use of the brakes. Yes, this may use slightly more fuel, but surely this outweighs the upfront capital expense of having to buy new brake pads prematurely?

    Therefore people must take these longer-term costs into consideration. As alluded to in the blog and in this comment, things are not nearly as simple as they are made out to be, and often the option with the most immediate benefits is not always the correct one.