SCMT

Sistema di Controllo della Marcia del Treno (SCMT) is a discontinuous train Cab signalling system used in Italy. It shares many features with the Ripetizione Segnali (RS) system, the two systems co-existing and working together. The main purpose of SCMT is to control the respect of the speed limit imposed by the signal aspect and the line condition.

SCMT is divided in two parts:

SCMT is based upon an array of transponders called "Punto informativo" (PI from now on) placed on the tracks near signals, reduced speed zones, and other important points along the line. The PIs form the SST. When a train passes over a PI, a set of "antennas" mounted in front of the first bogie energize it through induction. The PI then passes information about the aspect of the next signal through the aforementioned antennas to the SSB.

If the system is supported by RS, and if the signal shows a restrictive aspect (anything different from Green) it has to be acknowledged by the train driver by pressing a button, else the system just gives indication of the signal on its display.

The system then elaborates a "braking curve" (curva di frenatura), that indicates the speed the train has to respect during the approach to the signal, until the "target speed" is reached. Failure of either acknowledging signal aspect or keeping the speed under the imposed braking curve/target speed causes the SSB to command emergency braking, which lasts until the speed gets below the limit.

The SSB takes several variables into account, especially when computing the braking curve, such as:

As said before, SCMT is a discontinuous system; this means that it is not aware of next signals' aspect changes unless it passes upon the relative PIs.

E.g.: if the SSB gets informed by a PI that the approaching signal is "Yellow", it then automatically assumes that the next signal is going to be "Red" and elaborates a braking curve accordingly. But if meanwhile the signal becomes "Green", the SSB does not get aware of it, and it assumes that it is red until the train passes the next PI.

This does not apply if the Ripetizione Segnali (RS) is available (Only when the train is running on a BAcc block type line). In this case the two system work together, and since RS is a continuous system, the SSB is aware of aspect changes, while still appropriately elaborating the maximum speed the train can run.

SCMT has some benefits, in respect of the RS alone:

However, it has some disadvantages:

To partially solve the first two points, the "V-V-V" (stands for Verde-Verde-Verde) has been introduced. In practice, the distant, protection and departure signals of a station may be encountered by trains showing a green aspect (if some conditions are met), even if the train is scheduled to stop there, and thus is not subjected to speed restrictions imposed by the system.

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Wikipedia