The levels and operation modes are fundamental concepts of the ETCS system (European Train Control System). A short definition can be given as follows:
Level 1 involves continuous supervision of train movement (i.e. the onboard computer is continuously supervising the maximum permitted speed and calculating the braking curve to the end of movement authority) while non-continuous communication occurs between train and trackside, generally through Eurobalises.
Lineside signals are necessary. Train detection and train integrity checks (i.e. the train is complete and has not been accidentally split) are performed by the trackside equipment beyond the scope of ERTMS.
Level 2 involves continuous supervision of train movement with constant communication via GSM-R between the train and trackside.
Lineside signals are optional in this case, and train detection and train integrity checks are performed by the trackside equipment beyond the scope of ERTMS.
Level 3 involves continuous train supervision with continuous communication between the train and trackside. The main difference with Level 2 is that train location and integrity are managed within the scope of the ERTMS system, i.e. there is no need for lineside signals or train detection systems on the trackside other than Eurobalises. Train integrity is supervised by the train.
In addition, there are two more levels: Level 0, which applies to trains equipped with ETCS running on non-equipped lines; and Level STM, which is meant for trains equipped with ETCS running on tracks where the Class B system needs to be operated. With regard to the STM level, ETCS acts as an interface between the driver and the national ATP.
Operation modes can be defined as different conditions required for managing different situations regarding the status of the trackside and the train itself. Unlike the ETCS levels (associated with train-trackside communication), ETCS modes are related to the operational circumstances of the line or the onboard equipment status.
The main ETCS mode is Full supervision. The ETCS onboard equipment will be in Full Supervision mode when all train and track data, which is required for complete supervision of the train, are available onboard. In this mode, the onboard ETCS equipment is responsible for train protection (always ensuring that the maximum permitted speed and the end of movement authority are not exceeded).
There are also modes related to specific information that the trackside ERTMS subsystem can send, e.g. the Limited Supervision mode enables the train to be operated in areas where trackside information can be supplied to carry out background supervision of the train. In contrast to Full Supervision, in this mode, the information is simplified (especially the trackside Static Speed Profile) and the driver is responsible for the train’s movement.
There are also other modes for different operational situations. The following are some examples: shunting mode, on-sight mode (which allows the train to enter an occupied section) and a staff-responsible mode, which is a transition mode that allows train movement when it is acquiring data from the trackside under the driver’s responsibility