FrontPage 

Sources of information

Specific makes and models

I plan to use the next six months or eighteen months to choose a new car that is as ecological as it can be. I'll document my search for information here, and I'll be grateful for any additions anyone else can make, either in terms of technical knowledge such as the minutiae of CO₂ production, or sources of information, or reviews and experiences of specific models. 

September 2009

My current 2001 Fiesta will probably get through its next MOT in March, but probably won't manage the next one. So I plan to start gathering here as much knowledge as I can about what cars are on the market, and what their environmental effect is. The key thing is probably CO₂ emissions, but there are other factors such as ease of decommissioning, toxicity of metals and other products used, whether different spare parts have different environmental costs and so on. I haven't discovered much so far, but I have discovered it's not an easy thing to do. There's plenty of information out there, but we need to judge what the information is worth. For instance all cars now have an official rating for CO₂ emissions, expressed in grams per kilometre (g/km). I can discover very easily that my Fiesta emits officially 161 g/km, whereas the world's least belchy petrol car, the Honda Insight, emits 80 g/km. But consider the following.

I have kept figures over the whole of the Fiesta's lifetime. I have used 7800 litres of petrol to travel 80200 miles.  Mixing units is a real problem here. I get my petrol in litres and I measure my distance in miles. I still find it natural to think in miles per gallon terms, rather than litres per 100k. Those figures work out at 46.7 mpg.

The Honda Insight, when tested by The Register, averaged 49.8 mpg, not very different from my Fiesta, (as against its claimed 83.1 mpg). Now, for a start, when you consider that the Fiesta is nearly 10 years old, and the Insight is roughly twice the price, that's not a very good advertisement for electrically assisted driving. (Though I note that figures for real driving quoted on Wikipedia for the American version are substantially higher.)  And secondly why does it emit only 101 g/km as opposed to the Fiesta's official rating of 161. I don't know, and a little time spent trawling the net has left me not much wiser. I found this on WikiAnswers: "I think this depends on how good the engine is, since cars with similar mileage per gallon are quoted as having widely different CO₂ emission rates. Burnt under ideal conditions the figure is very close to 2.3 kg CO₂ produced per litre of petrol used. One litre of petrol weighs less than 1 kg however the additional mass comes from atmospheric O₂. Differences in result are introduced by many factors including: the quality of the petrol used, how completely the petrol is burnt, the measuring technique, and in an engine the age/efficiency of the engine, etc." So that suggests more research is needed on the circumstances under which petrol produces CO₂. As well as research on how the official figures are produced, because I find it hard to believe that engine efficiency can make 50% difference to the CO₂ production.

So, I need to look a lot more at what cars are available and at what kind of technologies are around, and may be coming on to the market in the near future. For instance, we await the Honda hydrogen-fuel-cell-powered FCX Clarity, not available here yet, in fact apparently not available outside California.  The Vehicle Certification Agency's Car Fuel Data page gives details of the ten best petrol and ten best diesel cars for CO2 emissions. The Honda Insight is top of the petrol list at the moment. I should consider diesel also of course, although the least polluting diesel is 107 g/km, a long way off the Insight's claimed 80.