Fixed train detection devices (GFM) are no longer required. As with ETCS Level 2, the trains locate themselves by means of positioning beacons and sensors (axle transducers, accelerometers and radar) and must also have on-board capacity to determine train integrity to the highest degree of reliability. By transmitting the positioning signal to the radio block centre, it is possible to determine at any time the point of the route which this train has already passed. A further movement authority for this point can then be granted to the following train. The route is therefore no longer cleared in fixed track section intervals, but using changeable intervals called moving blocks.

ETCS Level 3 departs from the classic operation with fixed intervals. With sufficiently short positioning intervals, continuous line-clear authorisation can be achieved. The spacing of trains follows the principle of driving in braking distance spacing.

The long-term objective is to develop the current systems in the direction of ETCS L3.