Selective Protective Points

SPP is the translation of Zwieschutzweiche. Berlin Lichtenberg station's Box B9 has two in this view. Basically these points are located in the middle of an M-shaped track configuration, where train routes can be set up over both legs at the same time, and therefore the point in question cannot provide flank protection for both routes. Although nowadays associated with computer controlled signalboxes, SPPs occured in old installations too.

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