The SZU: Sihltalbahn & Uetlibergbahn. It´s a standard-gauge adhesion railway wich has one (or the most?) steepest gradient in the world. The lines are integrated in the suburban lines of Zurich. The S10 runs from Zurich HB to Triemli and in less frequency further to Uetliberg. The S4 starts too at Zurick HB but diverges short time later to Adliswil, Langnau and then in less frequency to Sihlwald. The starting point of both lines is a two-track subway station with one platform between the tracks. Each track is used by one line as far as I know. After short way in tunnel, passing another tunneled station, we see daylight and the tracks running to Zurich-Giesshübel where the lines diverges. Here you can finde the depot and a "Highway" - a street that was build as bridge over a river - similar as the famous suspension railway in Wuppertal (Germany). The S10 increases slowly to the outer parts of Zurich to Triemli - the regular endpoint for most of the trains (single track platform), in less frequency (every 30min) a trains goes further up to Uetliberg (813m NN). The S4 runs to Adliswil and Langnau, with some trains further to Sihlwald. Mostly single track. The double track between Giesshübel and Zurich HB are as I know false double tracks. Every line uses here her own track, so it is basically single-track. And yes: both are very short lines: S4 ~ 14km (17, if extended to Sihlbrugg) and ~9 km on the S10. So I can understand if someone says: Too short. But: especially here it needs a good - a very good scenery building! In parts we can look over most of Zurich! Overall it needs lot of buildings, bridges and other objects, because the lines runs middle through the city, but also through forest. And we need a good landscape. And we would have basically 2 lines and 2 rolling stocks because there are used 2 different on both lines: an EMU, and a loco with doubledeck-waggons and a cabcar. For more infos. https://www.szu.ch/de/ueber-die-szu/sihltalbahn-und-uetlibergbahn/ https://de.wikipedia.org/wiki/Uetlibergbahn https://de.wikipedia.org/wiki/Sihltalbahn
