Big, booming cities are congested and polluted, and London, as one of the biggest and wealthiest cities in the world, is inevitably one of the most congested and polluted. With the world-leading congestion charge in place, and talk of extending it, the capital's traffic problems have so far received the most attention. But even the crusading London mayor, Ken Livingstone, admits there is a limit to how far traffic can be reduced. Attention is now focusing on the impacts of traffic, critically pollution and safety.
These are problems for everybody in the city, particularly the poorest: research repeatedly shows that deprived areas suffer most from stressful noise and vibration, bad air quality and road accidents. It is also a national issue: the size of the capital is so great that it has both an indirect - it could make or break national targets - and direct impact on the rest of the country. "We can see it through the ozone levels," says Tony Bosworth, transport campaigner for Friends of the Earth. "We can see, depending on the direction of the wind, that London is causing some of the pollution problems in the Home Counties."
London was a much dirtier city in past decades. As services replaced heavy industry, as engines got cleaner and as traffic stagnated due to congestion and, more recently, the congestion charge, pollution improved noticeably. Now London produces eight million tonnes of global-warming carbon dioxide a year, only 6 per cent of the national total and a fraction of the average. However, in terms of local air pollution, the capital is the dirty man of Britain - and indeed Europe - particularly when it comes to nitrogen dioxide and airborne particulates, the most dangerous pollutants. And according to the Greater London Authority's most recent environmental report, road traffic is "the major source" of these emissions.
Although Londoners with access to better public trans-port drive less than average, and buses are less polluting, the scale and density of the city dwarfs such advantages. The concentration of diesel trains and buses, and several major airports nearby, add to the problem. While the average national recording of high or very high pollution is 20 days a year, this rises to more than 50 days in parts of central London and to more than 30 even in some suburbs. The results are not just unpleasant - and uncomfortable for people with breathing difficulties - they can be fatal. Each year, 1,500 people in London are admitted to hospital for breathing-related problems. And in 1998, the Department of Heath calculated that 24,000 premature deaths a year in the UK were caused by air pollution; even if that figure has fallen with emissions, the toll is still enormous.
Then there are the more obvious victims - of accidents. Cinemas across Britain are currently showing a poignant ad featuring Sarah Rivers, a pretty and vivacious English girl who has made it big in LA, showing off her new lifestyle and luxury flat. But this is only a glimpse of what might have been: Sarah was killed crossing a road near her home in London before the teenage dream came true. "Don't die before you've lived," the advert says. The fictional storyline is affecting as it is; the statistics behind it are shocking: two child pedestrians are killed or injured on London's roads every day. In total last year, 6,000 people were killed or seriously injured on London's streets - and many more were injured less seriously.
It is hard not to think that, if motoring were "discovered" today, and the side effects foreseen, it would be run very differently, if not banned. "These are preventable accidents," says Rob Gifford, director of the parliamentary advisory committee on transport safety. "The incidents we're talking about are occasions where individuals make mistakes they shouldn't make. We wouldn't tolerate it on the railways, we wouldn't tolerate it in aviation, we certainly wouldn't tolerate it in medicine, yet we appear to tolerate it on the roads."
London's growing population and job market will increase travel in the capital and exacerbate these problems. So what is being done about it? The answer is that quite a lot is planned, but maybe not enough, given the continuing pressure of growth, and given that it is literally a matter of life and death.
So far, the mayor's most public proposal is to extend the congestion charge to encompass the western central area, and possibly out around Heathrow Airport. The original congestion charge, introduced in February 2003, was not - despite the rhetoric - expected to have a big environmental benefit, although the first-anniversary assessment claims some improvement. Calculations show that the daily charge has cut nitrogen dioxide and particulates by 12 per cent in the small zone itself, and by 2 per cent around the zone. But beyond that, as Transport for London admits, any benefits are unmeasurable. The national decline in accidents also appears to be proportionately bigger inside the zone - but again, it is too early to be sure. Extending the congestion charge zone would help, but the results are still limited by the desire for prosperity and growth.
"There's a Faustian deal, almost, between cities and some of those undesirable features of city life," says Tony Travers, director of the Greater London Group at the London School of Economics. "Clearly it will be possible, over time, for London and other cities to improve their environment. The trade-off is whether it can be done without damaging the economy, because Livingstone, as much as any other mayor, does not wish to harm the economy . . . He's growth with greenery, rather than greenery with growth."
Livingstone might not put it quite like that, but the point is recognised in another key proposal - a low-emission zone, which could exclude older and more polluting lorries, buses and coaches from the whole of Greater London by 2007, possibly followed by vans and taxis at a later date. The feasibility study estimated that this would cost industry between £64m and £135m to establish; it would cost TfL between £2.8m and £10m to set up and between £4m and £7m a year to run. In return, the health benefits in the first year alone would be worth £100m.
Finally, TfL has a wider strategy to improve the city's transport through the usual methods: making public transport more attractive, and encouraging walking and cycling. The current strategy probably underestimates the improvements to buses, forecasting that very small environmental advances will be offset by catering for the 800,000 more residents expected and more than 600,000 new jobs in just over a decade. The strategy promises "benefits" over the decade of £32bn in time savings, £6bn in safety improvements and £7bn in ambience measures such as comfort and cleanliness - but nothing quantifiable for the environment.
Commentators on all sides, as always, think more could be done - particularly in the politically sensitive area of curbing car use. As well as extending the congestion charge zone, Friends of the Earth wants more 20mph residential areas and greater road space given over to buses and to making cycling and walking safer - particularly around schools. Others want more 20mph zones, which the Transport Research Laboratory claims reduce death and serious injuries by between a third and half.
Certainly, something has to be done to reduce the long-term pressure of traffic growth and its problems, and this will require the support of national government in the form of allocating more funding, letting more of it be used for revenue rather than just capital funding, and working towards wider advances such as the longer-term goal of "clean" energy for electricity and transport. Environmentalists, and many local residents, also want government to curb airport growth, but a recent white paper does just the opposite. Which reminds us that while politicians and voters still value growth over green, we shouldn't expect too much too soon.
Juliette Jowit is transport and environment editor of the Observer