Division 7.2.1.1 General migration criteria

It is recognised that ERTMS cannot be installed on all existing high-speed routes instantly for reasons which include installation capability aspects and economic considerations.

In the transition period between the current (pre-unified) situation and the universal application of control-command class A interfaces^f1, there will be a number of interoperability solutions in the framework of this TSI, for both the European high-speed infrastructure including connecting lines and the European high speed trains. The unified concept recognises this and provision is made for modules known as STMs (specific transmission modules) to be added to the unified ERTMS system to enable a train fitted with appropriate STMs to operate over existing pre-unified infrastructure; alternatively an infrastructure may be equipped with both class A and class B^f2 systems.