The world`s first commercial magnetically levitated (maglev) train has started trial runs on a 30km-long track between Shanghai`s international airport and its financial district. The 430km/h train takes just eight minutes to complete the journey - compared to the 45 minutes needed to make the journey by road.

After the first public demonstration of the train, on New Year`s Eve, the German chancellor Gerhard Schroeder (seen above, left, with Chinese premier Zhu Rongji, right) revealed that the consortium that built the $1.2bn airport link, has now won a deal to build a further 300km of high-speed track. This contract, which could be worth $5bn, will extend the service south to Hangzhou, and north to Nanjing.

The Transrapid train (above), supplied by a consortium including Siemens, ThyssenKrupp and the German government, hovers about 10mm above the track and is propelled by what is, essentially, a synchronous linear motor. The consortium, subsidised by German tax-payers, has provided the trains, controls and power supplies, while China has built the track (through its Shanghai Maglev Transportation Development Company).

Although a maglev train operated for several years on a short track between Birmingham Airport and the National Exhibition Centre, the Chinese system is regarded as the first commercial-scale maglev project. Plans for a maglev link between Berlin and Hamburg were abandoned a few years ago because of the high costs.

After several months of trials and public demonstrations, the Shanghai maglev (shown above) is due to enter full service early next year. The Transrapid consortium hopes that the successful operation of the Shanghai link, which has taken less than two years to design and build, will help it to win contracts elsewhere, particularly in the US where maglev services are being mooted for several routes including a 60km line between Washington to Baltimore, and a 76km-long airport link in Pittsburgh.

There are also plans afoot for two maglev lines in Germany: a 37km-long track between Munich`s city centre and its airport which could carry eight million passengers a year from 2009; and a 79km-long line linking Düsseldorf to Dortmund. This line, which would include four stops on route, could carry an estimated 30 million passengers every year.

Another possibility is a 1,250km-long link between Shanghai and the Chinese capital Beijing, which could cost as much as $22-25bn. A maglev train would complete this journey in about three hours, providing a real alternative to air travel. But the Transrapid consortium faces competition for this contract from a rival 40-company Japanese group which is offering a more conventional system based on the Shinkansen "bullet train" technology. This would be slightly slower, but cheaper.

The maglev`s backers argue that their technology has several advantages over traditional wheel-based trains which could result in lower running costs as well as providing environmental advantages.

Most of these advantages stem from the way that the trains "float", suspended by attractive forces between electromagnets on both sides of the vehicles and stator packs installed below the concrete guideway. For example, because there are no wheels, gears, axles or current collectors to wear, maintenance costs should be low.

Another consequence of the design is that the vehicles are much lighter than conventional trains, allowing them to accelerate faster, to climb hills with gradients of up to 10%, and to negotiate tight curves. This, in turn, means that the track can be routed around obstacles, minimising the need to build costly tunnels, bridges and embankments.

The speed of the train is controlled by varying the magnitude and the frequency of the current in the stator coils. From a standing start, a Transrapid train takes just two minutes (or about 5km) to reach 300km/h. Its designers claim that modern wheeled alternatives would need more than 30km to reach the same speed.

Energy use is said to be a third less than a wheeled train, partly because of the much lower frictional losses. In addition, only that part of the guideway where the vehicle is passing is powered, and regenerative, non-contact braking is used to slow down the vehicles. Two vehicles cannot occupy the same section of track at the same time, thus effectively eliminating the possibility of collisions. Derailments are claimed to be impossible because of the way the vehicles encompass their guideways.

Another consequence of the lack of wheels is that noise levels are lower than those of any comparable means of transport, especially at speeds of 200-250km/h. At higher speeds, wind noise comes into play, but the noise levels at 400km/h are said to be no louder than a conventional train travelling at 300km/h.

Next year, the Shanghai maglev is expected to carry 10 million passengers, rising to 20 million by 2010.