Delivering compatibility between legacy Train Protection Warning System (TPWS) and ETCS is one of the most challenging elements of the rollout, but new technology is now available to make this a seamless process. UNISIG, the industrial consortium created to develop the ERTMS/ETCS technical specifications, has issued an Interface Specification for a unit they call a Specific Transmission Module (STM).
The purpose of the STM is to manage the interface between existing national train protection systems and ETCS to provide continuous train operation on sections not covered by ETCS.
