We're coming in by train, staying not far from the Mozartplatz, so we know we'll be getting off at the Mozartsteg bus stop right by the river on Rudolfskai. We also know that to get back to the train station, we just have to catch a bus on the other side of the river, probably at the Imbergstraße stop. The bus routes that hit both stops are the Red numbered 3, 5, 6 and 25. Also the green numbered 160, 170 and 175 - according to Google Maps.
A couple questions:
What's the difference between red and green?
Also, it's possible when we leave Salzburg that walking across the bridge to the Imbergstraße stop couldn't happen, so we'd just catch the bus at the Mozartsteg/Rudolfskai stop and ride the whole route, eventually arriving at the train station. But in the interest of saving time, do any of those routes go along Rudolfskai but cross the river right away at the Karolinenbrücke bridge and head right back to the station instead of carrying on who-knows-how-long before turning back? Google Maps just doesn't seem to want to overlay transit routes on the main map, but if I understand route maps like on Moovit, the answer's a big no..