###### Abstract
Euroloops play the same role than Eurobalises but they can transmit the data continuously over a particular section of the track. At this level, lineside signals are needed. * Level 2: this level makes uses of GSM-R to perform a continuous communication between both the train and trackside equipment. The lineside signal aspects and movement authority are displayed to the driver in the train cab. Out of the scope of ERTMS, other systems perform the train location using track circuits, axle counters, etc. At this level, lineside signals are optional. * Level 3: as level 2, level 3 uses GSM-R to perform continuous communication between both the train and the track. The main difference with level 2 is that the train integrity supervision and train location functionalities are performed by the ERTMS system. Thus, the train positioning is transmitted continuously allowing a continuous determination of the position of the train route that has been cleared. Thus, the route clearance is not performed at fixed track sections, as it happens in level 2, reducing the minimum headway between trains and increasing the transport capacity. ERTMS level 1 and level 2 have been implemented in many railway lines, not only in Europe, but also outside of European borders. On the other hand, real applications of ERTMS level 3 are still under test and development. While ERTMS level 3 becomes a reality, researchers are devoting efforts to develop the so called high density (HD) ERTMS to improve the transport capacity that level 2 provides using Eurobalises to divide track circuits [3]. Linking ATO to ERTMS is a good opportunity to solve the interoperability problems for ATO systems. With this aim, a TEN-T project [4] has been developed to include ATO in the ERTMS specification and the group of signalling companies, UNISIG, is working on it. The new ATO over ERTMS standard will specify the requirements that this system must comply to drive the train automatically and to be interoperable. Moreover, energy efficient operation is highlighted as one of the main goals of the ATO over ERTMS. Several projects develop complementary research activities to TEN-T project related to ATO in ERTMS context. Focused on freight transport, in the ARCC project [5] and in the FR8 RAIL III project [6], the train operation automation and smart data applications have been studied to increase quality levels, as well as energy and cost efficiency. On the other hand, methods to improve track capacity usage, energy efficiency, and punctuality by means of ATO systems are studied in X2 RAIL projects [7; 8; 9; 10]. It is expected that with ATO over ERTMS many real applications will be in service in the coming years. The Thameslink project in London developed by Siemens [11] announced the first commercial use of ATO over ETCS in March 2018. On the other hand, Rio Tinto announced in July 2018 the first fully autonomous heavy freight rail operation journey in Australia using the ATO over ERTMS system developed by Ansaldo STS [12]. Moreover, the ATO over ERTMS is being implemented in Mexico-Toluca line as part of a project that is under development by CAF Signalling [13]. The requirements of the ATO over ERTMS establish new functions that are usually assigned to human drivers. For example, speed control, accurate stopping, and door opening and closing. Different systems are needed to perform these tasks. Thus, it is necessary to differentiate between the trackside equipment and the on-board equipment. The trackside equipment is in charge of suppling the information of the track profile on the route, the operational restrictions and the timetable assigned to the train using specific ATO balises in ERTMS level 1 or via GSM-R in level 2 and 3 [14]. On the other hand, the on-board equipment is in charge of collecting all this information, generating the speed profile to fulfil the timetable, driving the train and informing about the train status.