What is a 'green' car?

There are many contributing factors in the so-called “well-to-wheel” scenario, including production issues and materials used, but for the sake of simplicity let’s concentrate on what goes in and what comes out of the car – the fuel and the emissions.

For all its sins, oil (petrol and diesel) remains one of the most efficient energy sources in the world and car-makers have made enormous strides in improving usage and emissions compared to even a decade ago, but the fact remains that oil is a resource that will eventually run out and will only get more expensive in the meantime.

There are a number of viable options on the table such as biofuels (made from plants and waste), electricity, ethanol, LPG (liquefied petroleum gas), CNG (compressed natural gas), hydrogen and even air. Some of these are available now, some are viable short-term, some are long-term prospects and some may never make it. But every car-maker is working on them.

In the meantime, the most obvious green cars are hybrids – cars such as the Toyota Prius, Honda Civic hybrid, the forthcoming Honda Insight and big luxury vehicles such as the Lexus RX450h and LS600hL (which still use plenty of fuel and are therefore not really green at all). But even the smaller ones are not necessarily the greenest cars available because, even putting aside contentious issues such as the energy required to produce the batteries and ship them around the world, small and simple turbo-diesel engines can use less fuel and emit even lower emissions.

Can a petrol-powered car still be green?

Yes. Modern technical developments – catalytic converters, electronic fuel injection, direct-injection, variable valve timing, electronic automatic transmissions, auto idle-stop function, cylinder deactivation, even turbocharging – have made cars much more efficient. In many big cities around the world, the air coming out of a modern leading-edge car’s exhaust is actually cleaner than the air going in. Even the most modest new cars are much better for the environment than older cars with outdated and worn-out technology.

Is diesel greener than petrol?

Generally speaking, yes. Diesels use much less fuel and therefore have lower harmful emissions, despite the image of smoke-bellowing trucks and buses. The direct-injection turbocharged diesel engines in modern cars are not only relatively clean and economical, but often perform better and can be more satisfying to drive than equivalent petrol engines. A classic example is the Mazda6 diesel, which is great to drive but uses only 6.0L/100km compared with 8.9L/100km for the petrol version. And modern diesel engines are much quieter than before, so you should barely hear the difference inside the car.

How do I buy green?

The simple formula for cars involves weight and power: The bigger and heavier a vehicle is, the more fuel it needs to accelerate or maintain speed. In terms of engines, energy equals power – the more petrol (or diesel or whatever) you pump in, the more power you get. Small equals green, so if the environment is your main criteria when buying a car, choose the smallest body and engine you can live with, regardless of fuel type.

The most obvious answer is to buy a hybrid car or a small diesel vehicle, or wait a couple of years for the first plug-in electric cars to arrive. That will certainly give you green credentials with your friends, but almost all those vehicles are small and may not suit your lifestyle. And the green value of electric cars will depend on the source of the electricity – we need renewable or clean rather than coal-burning power for this equation to work.

For bigger cars, consider the locally-produced LPG-fuelled Ford Falcon and Holden Commodore models, which come with a government rebate. Or have your car converted to LPG, which also attracts a rebate. LPG is relatively clean, but keep in mind your consumption will be around 30 per cent higher than for petrol, which will eliminate some of the cost savings from cheaper pump prices.

Under no circumstances should you buy an SUV or 4WD vehicle. They are much bigger and heavier than the vast majority of motorists require (not to mention the fact they hinder visibility for other motorists and don’t stop or handle as well as smaller vehicles). If you really need to go bush for the weekend, rent a Landcruiser. If you have more than three kids, there are wagons with third-row seating and relatively efficient people-movers like the Honda Odyssey and Renault Grand Scenic.

What can I do right now without having to buy a new car?

Simply drive better and smarter. The biggest saving we can make is driving less – planning trips better, combining trips, car-pooling, walking to the shops, even working from home one day a week if possible – but how you drive is also important.

Drive as smoothly as possible, accelerating gradually with a light throttle, reading the road ahead so you can back-off early for turns and intersections, judging the traffic lights. Every time you brake, you have to accelerate and use more fuel to get back up to speed. When using cruise control, accelerate slightly before hills rather than allowing the speed to drop, necessitating the car to accelerate hard and perhaps even change down a gear.

It is also worth filling up with E10, which most cars can use safely and contains 10 per cent ethanol, which in Australia is extracted from sugar cane.

Many people carry unnecessary weight in their vehicle, such as golf clubs and equipment that are only used occasionally, which adds to consumption.

In cool weather, only use the air-conditioning to demist the windows. With so many cars coming with set-and-forget climate control, many people are driving around these days with the AC running constantly without even realising.

Friction and wind drag also contributes more than people realise to fuel consumption and therefore emissions. Higher tyre pressures will help, especially on long trips, and also keep your windows up on freeways. Roof-mounted cargo fittings also create plenty of drag and could be removed if you don’t use them regularly.

Finally, keep your vehicle well-tuned. You may be amazed how much more efficiently your car will run after an overdue service.