Green motoring: an ABC

Know your hybrids from your biodiesel? Sean O'Grady explains the basics of eco-friendly driving

In case you hadn't noticed, tomorrow is "Green Wheels Day" and the Energy Saving Trust is promoting "Eco Driving", to encourage us to change our driving styles and eliminate fuel-wasting bad habits. The Energy Saving Trust, by the way, is a non-profit body funded by the Government and the private sector to encourage us to, well, save energy.

It used to run an excellent scheme called PowerShift which gave out grants for converting cars to greener energy sources, buying hybrid and electric cars, and that sort of thing. No longer, sadly, so the trust is reduced to issuing booklets with tips about greener driving. Laudable enough, but not the kind of incentive the motorist needs to take more radical action.

Still, here at Independent Motoring we're always prepared to do our bit, so here goes. According to the Energy Saving Trust you can help to improve your fuel economy and therefore reduce your emissions by up to 25 per cent without having to try too hard. This, we're told, is "eco driving".

First, the basics. Remember that more fuel-efficient cars cause less pollution and will save you money on fuel and tax. Cleaner cars, such electric vehicles and petrol/electric hybrids can also be exempt from congestion charging schemes (quite a saving if you live in London). Take CO2 emission levels into account. If you're buying a diesel car, choose one with a diesel particulate filter (DPF). And if you want a Lamborghini, then maybe a Mini Cooper S, our main Road Test feature, might offer some of the same thrills with less damage to Mother Earth? Well, it's just a thought.

Hybrid vehicles are a particular case in point. They've come under some criticism because their official government-measured fuel consumption figures are even less realistic (ie, worse) than those of other cars. That presumably means their CO2 numbers aren't as good either.

Hybrid cars have a conventional engine and an electric motor which runs on batteries that are recharged while you drive, so you don't need to plug them in to top them up. The Toyota Prius, Honda Civic Hybrid and various Lexus cars run on petrol and electricity and other diesel/electric models are expected.

As to whether hybrids are more efficient than a well-engineered diesel engine (the best seem to be made by Peugeot/Citroën and Toyota) is debatable. It depends on the circumstances. The more urban driving you do the better, because the weight of the batteries compromises the cars' economy at higher speeds or harder acceleration. The Independent has run the Prius and Civic Hybrid as long-term test cars and found that the Civic gave about 39mpg and the Prius anything from 45mpg to 55 mpg (it gets worse in winter), much less than the official numbers in the 60s for mpg.

Electric vehicles, by contast, produce no tailpipe (exhaust) emissions (and comparatively little, indirectly, at the power station). Most, however, have limited performance and range. The electric Smart is worth waiting for if it does indeed go on sale to the public next year, as the company suggests. Otherwise there's the Reva G-Wiz.

You could try an alternative fuel. Produced from plants, or less commonly from waste cooking oil, biodiesel is a diesel substitute that reduces emissions. All diesel cars can run on 5 per cent biodiesel (a ready blend of 5 per cent biodiesel and 95 per cent conventional diesel). Using blends of more than 5 per cent biodiesel invalidates most manufacturers' warranties. You can even run a supercar on it (see feature on Iceni Trident R, page 4).

Bioethanol is similarly greener than fossil fuels. Produced by fermenting plant material, bioethanol is a petrol substitute that reduces overall CO2 emissions. All petrol cars can run on 5 per cent bioethanol (a mixture of 5 per cent bioethanol and 95 per cent petrol). But you should only use blends of more than 5 per cent if your car has been specifically designed to run on ethanol (Ford and Saab offer models that do so).

But you can start saving the planet the minute you next get behind the wheel. Try, for example, to check your revs - next time you change up a gear, look at your rev counter (if you have one). If you're driving efficiently, you should be changing up at no more than 2,500 rpm in a petrol car and 2,000 rpm in a diesel. Keep to 60mph, as beyond that the amount of fuel you use goes up considerably. Driving at 80mph instead of 70mph uses up around 10-15 per cent more fuel. If you're stuck in a traffic jam, at a railway crossing or waiting for someone for more than two minutes, turn your engine off.

Check your tyre pressures and travel light. Eco driving can even be fun, as you try to eke out the maximum economy from your vehicle (as opposed to performance). At least you won't feel quite so guilty in your Lamborghini.