By Tom Symonds Transport correspondent, BBC News

Tom Symonds' car produced a third more CO2 at 80mph than at 70

Is it possible to save the planet by sticking to the speed limit? The government's transport advisors think so.

The Commission for Integrated Transport argues that emissions from cars and lorries still outweigh by some way those from air travel, though aviation is growing as a source of carbon dioxide.

One remedy, the authors conclude in a report published on Wednesday, is for us drivers to have state-sponsored lessons in eco-motoring, an idea that would cost the government little but benefit the planet a lot.

The theory is that the way you drive can be as important as what you drive, and how much you drive it.

Smooth driving

By way of an experiment, we went to the Ford test track at Dunton in Essex, to break the speed limit.

Drive at 80mph on a motorway and it is claimed your car will pump out significantly more carbon dioxide than at 70.

With a technician plugged into the car's engine via a laptop, I drove a series of laps, maintaining 70 and then 80 on the two straightest sections.

The result? The car produced a third more CO2 getting from one end of the track to the other at 80 than it did at 70.

Our own analysis indicates that a driver can save around 25% of fuel consumption in a year Andy Taylor, sustainability director for Ford

But there's more. Research suggests turning on the air conditioning uses 10% more fuel, therefore producing CO2.

Unfortunately keeping cool by lowering your car windows also increases fuel consumption, as does keeping the roof rack on after that family holiday.

Most of all, driving smoothly is the key to an environmentally-friendly motoring life.

Gentle on the accelerator, thinking ahead, judging the distance to the lights, and stopping without a jolt.

Ford's director of sustainability Andy Taylor says: "Our own analysis indicates that a driver can save around 25% of fuel consumption in a year.

"That will save around up to �200 a year, helping your wallet, but also making a material difference to the planet. At the end of the day for the vast majority of people, it's about the money."

However, the Commission for Integrated Transport (CFIT) wants action from companies like Ford as well as its customers.

By 2020, its report says, all cars should produce no more than 100g of CO2 per kilometre.

In other words, they'll all have to be roughly as green as the greenest production cars are now.

Flight taxes

Aviation doesn't escape either. Emissions trading - which forces airlines and airports to buy the right to produce CO2 - is a must, the report concludes.

And the government should be actively finding ways to make flying more expensive.

CFIT quotes a new Mori poll which suggests a growing number of air travellers accept the idea of higher taxes.

The commission's strategy is to find ways for the government to get more environmental bang for its buck.

It has predicted the measures would increase by 70% the CO2 savings proposed by the government's climate change programme.

In other words, the report says, the current plan to stabilise carbon emissions by 2020 would become one to reduce emissions by around 14%.

But the findings make clear there is a need for action at all levels - from the government, from companies, and from us, sitting at the wheel of our cars.