By common consent, about 80% of the energy a car uses in a its lifetime is down to the fuel it burns to make it move.
That means a hefty 15% goes into making the car, designing and developing it. The final 5% is used up in recycling it.
So, to a car buyer interested in making a green choice, should that manufacturing percentage matter?
Yes, says the Environmental Transport Association (ETA), which tries to give car buyers advice from a green point of view.
Andrew Davis, the ETA's director, says: 'It does matter, and we try to bring it to people's attention, but we would stick to our usual advice and say buy the simplest, smallest car for your typical usage. Such a car wouldn’t use as much energy to produce as a more complex one.'
Getting detailed information on how much energy is used during the manufacturing process is very difficult. Very few car makers publish figures - Volvo is an exception - largely because building up an accurate picture of how much energy is used in the thousands of different components and in factories is fiendishly difficult.
When the subject became popular in the 1990s, at the time environmentalism got into its stride, Volvo embarked on a detailed study of energy used in every part of its cars.
The project was abandoned when it became clear it would grow so big that the numbers couldn't be calculated meaningfully.
Like every car company, Volvo shifted its environmental concerns to global warming and tailpipe emissions of carbon dioxide.
On manufacturing energy, Volvo did what most car makers have done, and accepted academic research from the late-1990s that came up with the 80/20 rule – 80% of energy used in fuel/20% in manufacture/recycling.
That figure has more recently been challenged by an American market research company called CNW. Their investigation turned the 80/20 figure on its head and suggested the exact opposite.
What did the CNW report say?
The accepted wisdom is that all cars use up the same amount of energy as they are built, regardless of their size or in which country they are produced. However, after sending researchers to factories in Japan and Europe, CNW came up with the remarkable finding that traditionally built vehicles, such as Jeeps and big 4x4s, use a lot less energy to produce than high-tech green vehicles, such as the Toyota Prius.
Indeed, the research suggested that so much less energy is used in their construction, that their poor fuel economy is cancelled out. CNW's report has attracted its fair share of detractors, however, and Toyota, of course, disputes this finding.
It's difficult to decide which side is right in this argument, because there are no comparative figures from an independent body. What the CNW study has shown, though, is that car makers cannot simply consider tailpipe emissions alone when they are designing and building cars. They have to make sure their manufacturing processes limit energy usage so they can deliver a truly 'green' car.
Click here to see the full table of CNW's results.
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