The exit signals of Preda station in the direction of Bergün (Thusis-Chur)

You can switch from the nearest track to the other but cannot come back. There is no need though, it's a double-track section with about 1.5 km of double track. The Albula REX trains stay by the platform about 2-3 minutes at every passing station (Thusis, Filisur, Preda), so they could manage without the double-track islands, but because trains are very long (clearing the track takes a lot of time) and 1 or 2 minutes of delay may gather even in Switzerland the double.-track sections provide for the necessary flexibility in the timetable to keep it punctual.