Topic of the Month: Archive

Topic of the Month: Should you keep your old car or buy a new, efficient one?

Here is the product of our first Topic of the Month…..thank you to all who contributed.

Should you keep your old, petrol guzzling car, or trade it in for a new, efficient one?

There’s a lot of data you may wish to consider.

You could start by looking at the following….

The website of the "Vehicle Certification Agency" (VCA) is helpful ( ). It has good general background information to the issues, plus, if you want detailed information on fuel consumption and exhaust emissions for any car, they have the official figures for all cars admitted on UK roads in the last 10 years or so (not just for new cars as is the case on most other websites). Even better, the downloads section makes all the data available as spreadsheets and in other formats! 


Click  here for the official site for comparing new cars based on CO2 emissions.


What Car? Has a green car guide at including a second-hand buyers’ guide at


Here is the “official” FOE view: - a bit lacking in real information for most car buyers…

There is an in depth discussion of embedded carbon here

…….and a more applied analysis here

We seem to be able to say…


1.       The embedded carbon in a car will be replicated in about 2 years of average use (12,000 miles pa)

2.       Cars with complicated engines and batteries (like Prius) have much higher embedded carbon

3.       So, if your mileage is low, say 2000 miles pa, then there is significant carbon benefit in keeping your old car – you are unlikely to emit enough carbon over the life of the car to equal the embedded carbon in the new car.

4.       If you do average mileage and your new car has 25% lower CO2 emissions, if my maths is correct, it will take 8 years for you to compensate for the embedded carbon in the new car- perhaps more if you have gone for a car with high embedded carbon.

5.       It would seem that the arguments for trying to buy a fairly efficient second hand car, rather than a new car, are good

6.       Obviously, the more mileage you do the better the arguments for going for a new car.


Do let me know if you have anything to add!