It would be greener and cheaper for many motorists to keep their car for as long as it is reliable rather than trading it for a new car, according the Environmental Transport Association (ETA).

Before a new car has even been turned on, before it even leaves the showroom, it has already accounted for 6 tonnes of CO2 emissions just in the construction, delivery, and marketing.

A spokesperson for the ETA said: "Swapping a thirsty and polluting older car for a lighter, more fuel-efficient model can make environmental sense if you are doing a high mileage, but if you do relatively few miles it makes sense to keep your car for as long as it is reliable. The greater your annual mileage, the greater the potential environmental saving from changing to a more fuel-efficient model."

How to get better gas mileage with the car you already have:

Don't drive aggressively.

If you stay cool and collected behind the wheel, you aren't just doing wonders for your blood pressure, you're saving an astounding average of 31 percent on gas. When you're on the highway, stay in one lane and cruise at a moderate speed and you'll be shocked at the results.

Use cruise control.

Using cruise control on longer trips can save an average of 7 percent on gas. Again, just get in the slow lane and cruise, it's well worth it. Don't submit to peer pressure that says you have to speed up.

Change your air filter.

If your air filter is dirty enough that when you hold it up to a light bulb you can't see much light through, then it is time for a replacement.

Change your oil.

This is one that you may or may not be your cup of beans, but if you do, just make sure that you buy an oil container large enough to handle the capacity of your vehicle's oil and then take it to a recycling facility. Check out more ways to save gas on Planet Green.