China does not usually attract much notice at the North American International Auto Show in Detroit. But mainland carmaker BYD has caused quite a splash at the annual car show this week. As we report on our Motoring page today, it is showing a purely electric car with a driving range, on a single charge, of 400km. This puts it on par with some of the world's major manufacturers, such as Ford, GM and Toyota, all of which are, belatedly, introducing their own electric cars in North America. The success of BYD, in which world-famous investor Warren Buffet holds a substantial stake, shows what many have argued about China: because it is developing so many industries and building new cities, it is in a much better position to quickly adopt clean and green technology than many developed economies. At the moment, however, the signs are not good. The nation's transport boom is posing a growing challenge to the environment. More than 84,800km of highways are being laid across the country. The number of cars on its roads grows by 14,000 every day. By the end of the next decade, the mainland will have 130 million cars. At current rates, the number of cars on its roads will exceed the number registered in the US sometime between 2040 and 2050. The nation must start promoting hybrid and electric cars, otherwise vehicles will surpass coal-fired power stations as the biggest source of air pollution. But China can have a greener future. As the major oil companies and most carmakers are state-owned, it is much easier for the central government to make them launch, by fiat or administrative means, initiatives in the use of alternative energy and environment-friendly vehicles. Unlike Hong Kong, where relatively few people own cars, the mainland has a potentially large market and the necessary economies of scale to make 'green' car production commercially viable. As highways are built, service stations mushroom. This provides an opportunity to establish a nationwide service infrastructure - with chargers for electric-car batteries and battery-replacement services. Already, several big cities have experimented with electric buses and minivans, but they have not made the transition to mainstream service. Municipal authorities should be given incentives to do so. China has an opportunity to set itself up as a pioneer in electric vehicles. Indeed, given the worrying levels of its pollution it has no other choice.