The train control system used in Switzerland at present (ZUB) was designed on the basis of an analysis of hazards, i.e. additional safety measures were implemented at high-risk signal locations to monitor trains by means of a braking curve. All other, (less hazardous) locations, are equipped with warning/stop signalling (SIGNUM).

ETCS Levels 1 and 2 are not scalable, i.e. all route locations have to be equipped with speed monitoring in “full supervision” mode. It is not, therefore, possible to implement simplified supervision of the type currently used.

Together with other railways, SBB submitted a change application to the European supervisory authority, AEIF, requesting a “limited supervision” mode. ETCS Level 1 Limited Supervision (L1LS) permits scalable functionality whereby each signal location can be equipped to the desired safety level.

It is anticipated that the Limited Supervision mode will be incorporated into the ETCS standard as part of a regular release upgrade to SRS 3.0.0.