ROLL-OUT of Germany's first driverless metro has been delayed again, and commercial services on Line U3 of the Nürnberg U-Bahn are not now expected to start until early 2008.

Contractor Siemens had intended to have the first segment of U3 ready for operator VAG to open in 2006, but the supplier has since conceded that the Rubin project (RG 2.05 p85) was far more complex and time-consuming than it had anticipated.

While the automation technology is based on the proven concept of inductive loops between the rails to transmit data between train and track, Rubin is certainly not straightforward.

The project includes the ambitious objective of running a mix of driverless U3 trains and manually-driven U2 services over a common section of route between Rothenburger Strasse and Rathenau Platz. U2 services already run at 200?sec headways, and U3 will ultimately do likewise. This will require 100?sec headways, which is only achievable with automation.

A mechanical problem with the car structure of the two prototype DT3 trainsets proved serious enough for VAG Nürnberg to return the trains to the supplier, which inevitably delayed the trials programme. Only last November had enough progress been made to start limited testing with empty driverless trains mixed with manually-driven trains carrying passengers.

Siemens also underestimated the time needed to put in place and test the profusion of alarms and detection devices. As no platform screen doors are fitted, high-frequency intrusion monitoring devices are used to check for objects or people falling on to the track. Cameras monitor the tunnel ends for intruders, and the driverless trains are fitted with obstruction detectors. Each bogie also has a derailment detector. All these systems are linked to the automation and train control equipment that can initiate emergency braking.

Complexity is further increased by automated plates at each doorway that bridge the gap between train and platform, to say nothing of a comprehensive fire detection system which meets the tough regulations introduced following the disastrous blaze on the Kaprun funicular in November 2000.

With the revised opening date less than a year away, VAG and Siemens still face a demanding task in proving to the German safety authorities that Rubin works satisfactorily.