In Level 3, ETCS goes beyond the pure train protection functionality with the implementation of full radio-based train spacing. Fixed train detection devices are no longer required.

As in ETCS Level 2, trains monitor their position themselves by means of positioning beacons and sensors (axle sensors, accelerometer and radar) and must also be capable of determining train integrity on-board to the very highest degree of reliability. By transmitting the positioning signal to the radio block centre it is always possible to determine which location on the route the train has safely reached. The following train can already be granted another movement authority up to this point. The route is thus no longer cleared in fixed track sections.

In this respect ETCS Level 3 departs from classic operation with fixed intervals: given sufficiently short positioning intervals, continuous line-clear authorisation is achieved and train headways come close to the principle of operation with absolute braking distance spacing (“moving block”). Level 3 is currently under development. Solutions for reliable train integrity supervision are highly complex and are hardly suitable for transfer to older models of freight rolling stock.