In the French capital for Michelin's annual low-fuel vehicle rally, Ruth Brandon considers the options for tomorrow's motorised transport

In 1998 Bibendum, the bouncy Michelin man, was 100 years old. To celebrate his centenary, Michelin decided to inaugurate an annual rally that would showcase environmentally friendly vehicles. And that, Michelin points out, includes tyres: if every car and truck in Europe were fitted with "green" tyres, around 4.5 billion litres of diesel and 1.5 billion litres of petrol would be saved every year.

Over the years Challenge Bibendum has visited California, Germany, Shanghai and Kyoto. This year it was in Paris, ending up at the Eiffel Tower: a vast assembly of manufacturers, researchers and government officials, all milling around 159 vehicles boasting the latest in low-pollution, low-consumption propulsion techniques. It's a weird experience: lots of cars and trucks driving around and not a whisper of engine noise. One Challenge veteran I spoke to declared it the most dangerous event of the motoring year - all those trucks driving about, and you can't hear them coming. I foresee a booming market in ringtones.

Most of the technologies are already familiar, if only from the motoring pages - battery electric, hydrogen fuel cell, hybrids, ethanol and biodiesel engines.... Of course, not all the vehicles on show are yet in production. But they're a foretaste of what's coming, as well as reminding us of what's here, if not necessarily yet parked by a kerb near you.

Along with the novelties, we saw better ways of using what's already there on the forecourt. The internal combustion engine is monstrously inefficient - only 25 per cent of the petrol's potential energy ends up pushing the wheels round. Now direct-injection, where the petrol is injected into the cylinder as in a diesel engine, can substantially increase this efficiency, and is coming on-stream.

But why use petrol at all? In Brazil, 95 per cent of all new vehicles sold now run on ethanol or biodiesel. Of course, new vehicles does not mean all vehicles - the car fleet takes 15 years to renew itself. So as an increasing variety of new fuels become available, one of the most important technologies is going to be flexible fuel engines that will allow you to fill up with whatever happens to be there - liquid natural gas, liquid petroleum gas, ethanol, vegetable oils, or unleaded petrol and ethanol in any combination from pure petrol to 85 per cent per cent ethanol. The filling stations of the future will offer more than just petrol and diesel - and if you pick the wrong pump, you can relax: whatever it is, it won't ruin your flex-fuel engine. Biofuels, since ce they use up land that could otherwise grow food, will never supply more than 20 per cent of the world's fuel needs. But there are other possibilities. Synthetic petrol can be made by a process using carbon sequestration. And of course, there's hydrogen. But although everyone agrees that some form of hydrogen will eventually run cars, there is disagreement about whether this will involve using it as itself - for instance as a reactant, with oxygen, in fuel cells - or as a base product from which to manufacture synthetic fuel that would be easier to produce and distribute.

Battery-electric is of course as venerable as the internal-combustion engine. It's no panacea - its range and speed are limited, though both are now immensely improved, and of course it only displaces pollution, from the city to the power-station that must make the electricity in the first place - although pollution may well be much lower in scale. And if that power-station runs on gas, then it's a monstrously inefficient was of using the available energy. That said, pollution and the price of fuel are bringing ever-increasing numbers of electric cars on to city streets. The constraints of accommodating all those batteries and keeping the vehicle light mean that many of them are notably unglamorous. But two of the most spectacular vehicles on show in Paris were electric cars designed by Courrèges, who made his name putting Sixties dolly-birds into kinky white boots. Handbag cars but if you're going to buy a handbag, why not get a couture model?

Meanwhile a range of technologies are waiting in the wings. Compressed auto-ignition is pollution-free - an important improvement, as cars emit maximum pollution on and just following ignition. Plug-in hybrids will allow you to travel 10 or 20 miles just on your electric engine, before the internal combustion engine cuts in to recharge the batteries. And synergy hybrids, using electricity and biofuel, will give us the best of all emissions worlds.

I particularly liked the Smarts, designed with interchangeable modular engines, so that you can choose between petrol, diesel and hybrid. The hybrid, however, will cost £3,000 more than the others, mostly because its electric engine is very small, and accordingly expensive.

This is important stuff. Until recently, transport planners had been hoping that various sticks and carrots - high fuel prices, pollution, traffic jams, better public transport - might coax us out of our cars. But research seems to show that although some movement can be engineered, it is, even at best, relatively insignificant. So, faced with oil depletion and climate change, new technologies such as these are vital if we are to keep wheeling and prevent ourselves frying.

In that sense, this year's Challenge Bibendum was enormously heartening. Technically, there's no doubt we can do it. But the big question still remains. How do we get people to use all this stuff? And when? How many people do you know who drive a hybrid or an electric car?

And how can we persuade people to switch fuels if they can't be sure of finding an appropriate filling-station when they need to top up? Southern California, now as ever the world leader in new automotive technologies, already has a "hydrogen highway". But that consists of only 23 hydrogen stations. The existing petrol infrastructure has taken nearly a century to set up, and no one has really begun to plan an alternative one.

This is partly because no one is yet sure what it will carry. It's a chicken-and-egg question. Without the infrastructure, people won't buy the cars. But until they do, it's not worth putting in the infrastructure.

Should governments be doing more to encourage change? At the moment it feels as though they could hardly be doing less. But although they can help - by taxation policy, and by using innovatory technologies for public service fleets - the market is the real force. The big question is whether change will be gradual or whether there will be a sudden tipping point. That's what happened in Brazil, where five years ago, only a few thousand new cars ran on ethanol. The sense at Challenge Bibendum was that the market is on the point of changing. And the smart money is keeping ahead of the game.

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