Division 7.2.1.2 Use of class B systems for interoperable trains

In a migration phase from pre-unified national systems to the unified system, if only part of the fleet is equipped with an on-board system able to handle the unified system according to class A, it may be neces-sary to have both systems fully or partially installed on a stretch of line.

There is no functional link between the two on-board systems except to manage transitions during train operation (and as required to satisfy the needs of the STMs for class B systems when STMs are used).

From a purely functional point, a system may also be built combining components from the unified and a pre-unified system. An example is the combination of an ERTMS/ETCS system level 1 using Eurobalise as a spot-transmission means and an infill function not based on a unified solution, but on a national system. This solution requires a data link between the unified and the pre-unified system. Therefore, the solution is not in accordance with either class A or class B. It cannot be declared interoperable.

There is, however, the possibility to use the combination as a national enhancement of an interoperable line. This is only permitted if trains not equipped with the data link between both systems can operate either on the unified or on the pre-unified system without information from the other system. If this is not possible, the line cannot be declared interoperable for the control-command subsystem.