CURRENTLY ON trial in China are two new Plasser & Theurer tamping machines which will revolutise infrastructure maintenance on the rapidly-expanding Beijing metro network.

At present there are four lines in operation - 1, 2, 13 and the Batong Line, with a total route length of 114 km. Including the five rolling stock depots these lines have 390 turnouts. Four more lines (5, 6, 10 and the Airport Line) are due to be completed in time for the 2008 Olympic Games, bringing the network up to approximately 200 route-km.

During the Olympics the metro expects to operate around the clock, requiring availability close to 100%. The metro's infrastructure department has already started planning a programme of enhanced maintenance work to ensure the network is in optimum condition ahead of the event.

Given the small time windows available for maintenance, Beijing Metro decided to invest in modern technology to increase the amount of work achieved each night. Improving the accuracy of track maintenance would give a longer service life and extended maintenance cycles. To this end it needed specialist machines suitable for a smaller metro loading gauge and third-rail electrification, but with a proven peformance record.

After looking at the market, the metro decided to buy two Plasser & Theurer 08-16 SP4 CH tamping machines. The Austrian firm was already supplying track maintenance machines for the main line railways in China, and had also supplied similar machines for urban operators elsewhere.

The 08-16 SP4 CH has four split-head tamping units, which can be used as a group or separately. Two of the tines in each set are tiltable, making the machine very versatile for tamping switches. The lifting and lining unit is equipped with rollers for high output rates when working on plain track and a special lifting hook for working on turnouts within the restricted space of metro tunnels.

The latest generation ALC (automatic guidance computer) control system is ruggedised for protection against moisture and shock, promising high reliability. Driving cabs are provided at each end of the self-propelled machine, which can run at 80 km/h to and from the worksites, and operate on gradients as steep as 3·4%. MOR standard buffer beams and centre buffer couplers are provided at each end, allowing the machines to be towed in-train at up to 100 km/h.

Built at Linz and assembled in China earlier this year, the machines are now undergoing final commissioning in Beijing, and are expected to start operation within the next few months.