ETCS Level 2 and 2+: Capacity with a safety net

In Level 2, the train registers with the Radio Block Centre (RBC) and continuously reports its position and direction. The RBC evaluates the route data reported by the interlocking - including signal aspects and point positions - and adds track data. The result is the Movement Authority: the digital authority to move, with an end point, speeds, gradients and further supervision data.

This authority reaches the train via Euroradio. The on-board computer derives braking curves and supervises the journey; in Level 2, Eurobalises mainly act as robust position references. The division of roles matters: the RBC complements the signalling system; it does not replace the interlocking. Conventional track-vacancy detection generally remains in place. Level 2 is therefore not a moving-block system, but highly digitalised train control on infrastructure that is still physically supervised.

Level 2+ is not an additional formal ETCS level. Here, the term describes measures that raise the capacity of a Level-2 line. Hybrid Train Detection (HTD) is a clear example: a conventionally, physically detected block is divided into virtual sub-sections (VSS).

These VSS have no physical track-vacancy detection of their own. They can therefore be released logically only when the leading train reliably reports its train integrity. A train without such an integrity report can still use the line, but it does not unlock the benefit of the virtual subdivision. Once clear, the overarching block is still released physically. This provides a valuable fallback in the event of radio loss, a missing integrity report or an RBC restart.

The idea behind Moving Block goes further: rather than fixed block boundaries, the current position of the train ahead determines the protected distance. In the classic Level-3 concept, track-vacancy detection would follow from train position reports. That requires train length, position and integrity to be reliably known in every operating situation.

This is where the technical and operational challenge lies. Position reports are cyclic; according to the underlying introduction, intervals below six seconds are unrealistic. By the next report, a fast train may already be well beyond a relevant boundary. Odometry uncertainty is an additional factor and depends on the vehicle, weather and balise layout. Capacity projections therefore need to account for the adverse case - not merely the idealised diagram.

The benefit is real, but not magical: compared with a well-optimised Level-2 line with suitable block spacing, the additional gain from Moving Block alone is often small, according to the source. The result can differ on lightly used regional routes. HTD is therefore a pragmatic intermediate step: shorter headways where integrity data are available, without giving up established physical track-vacancy detection entirely.