In the UK alone, we cover a staggering 321 billion kilometres a year in our cars (source: DETR Transport 2010:The 10 Year Plan). If you think that the congestion and air pollution we currently put up with are bad, then what will things be like by the end of the decade, when these numbers are expected to be 20% higher?

Even if you ignore the damage to the environment and our health that can be attributed to the private car, the financial costs resulting from the pollution and congestion are phenomenal. So why don't we do something about it?

The usual response is that there is no alternative. Public transport is a joke, and anyway, car ownership is not only a measure of our status, but also a right. Oh yes, and cars as fun.

Whether you agree with those views or not, the plain facts are these: while we need to get around, our current car use is not sustainable. We need to do something.

So, hats off to car manufacturer Kia. Whatever else you think about the company or its products, they deserve credit for recognising that we have to modify the way we use private cars and for backing initiatives like Walking Bus. MG Rover, meanwhile, appear to have decided that having a social conscience doesn't sit with their brand image. Having been forced to withdraw ads last year by the Advertising Standards Authority because they were seen to encourage speeding and unsafe driving (see BBC news item), they now use the slogan 'life's too short not to'. Come on MG; be a force for change before change is forced upon you.

Change such as that taking effect from April 2002. In April the Inland Revenue will introduce a new system for calculating the value of the benefit of having a company car. The charge will be based on the car's carbon dioxide emissions and the existing reductions for business mileage and older cars will no longer apply. See the Inland Revenue site for more details.

State and regional governments in other parts of the world are also taking action. As Guardian Unlimited reported last week, Italy's Lombardy region, one of the industrial powerhouses of Europe, is planning to ban the sale of new petrol- and diesel-powered cars as part of a unique and ambitious clean air programme unveiled by the region's president.

Driven by a smog emergency caused by two months without rain, Roberto Formigoni has challenged car manufacturers to come up with alternative "green" vehicles to meet a deadline in three years.

Fiat, BMW and Citroen have already responded to Mr Formigoni's appeal and officials from the three companies will soon present proposals to the region's technical experts.

Mr Formigoni is confident that his plan is feasible, as it enjoys the support of central government and two-thirds of the region's citizens.

California has more to do than most. Its cars are responsible for nearly 4% of global carbon dioxide emissions, but this week it could take the first steps towards limiting emissions from cars and light trucks. (source Environmental News Network).

The bill in question, proposed by Bluewater Network, a San Francisco-based environmental group, faces strong opposition in the state Assembly, but is backed by those who see this as a chance for the state to take a lead in dealing with this issue.

Back in the UK, should we write off public transport completely?

Guardian Unlimited reports that Nottingham could provide a model for the future of British transport. It has regular trains, punctual bus routes, a planned tram system and the airport is a quick drive from the city centre.

Nottingham City Council and Nottinghamshire County Council have been praised by the Government and the two authorities have worked closely for years on strategies to improve public transport and keep traffic moving.

The European Commission regards the area as a pioneer in developing 'green' commuter plans, where local employers encourage workers to leave their cars at home by subsidising bus services, providing showers for cyclists and organising car-sharing schemes.

Although not perfect, Nottingham is leading the way in showing the rest of the country what is possible.

What do you think should be done, if anything, to reduce our car use? Should we focus on making cars cleaner, or try to persuade people to save the car for essential journeys only? Use our comments page to let us know.