The present document constitutes the Deliverable D 5.4 “Sample architecture for Automation of Legacy Mainline Locomotives” in the framework of the FR8HUB WP5 task 5.10, of the running FR8HUB consortium within Shift2Rail Innovation Programme 5 (IP5). The deliverable has been added to the Fr8Hub WP5 scope in the final phase of the Fr8Hub consortium as a scope extension, in order to highlight to the European Freight community, that automation opportunities are not restricted to shunting operations but also concern the legacy mainline locomotive fleet, as tested in IP5 in 2020.Inside Shift2Rail the technology demonstrator TD5.1 “Fleet Digitization and Automation” and more precisely TD5.1.3 “Freight ATO/ DAS” it has been planned to test and promote interchangeable and interoperable solutions for freight automation in operations of the legacy fleet, to gather first practical experience with automated driving of freight trains. The Automated Rail Cargo Consortium (ARCC) has achieved a major milestone in this regard in 2020. Based on the experience made by ARCC but taking an appropriate step back towards a more generic standpoint overlooking the legacy fleet, the D5.4 presents a simple starting point for automation mainline locomotives in Europe. The purpose of this document is to deliver a possible sample architecture for automated train operation of mainline rail freight locomotives, as an additional innovation capability, on top of the shunter automation described in Fr8Hub D5.3. Leader of this Deliverable: DB Cargo AG