The Elbe bridge Bad Schandau (B172) is fully closed for safety reasons. This also applies to pedestrians and cyclists!
Travelling by car:
The large-scale diversion is via the Elbe bridges in Pirna.
Travelling by train:
S-Bahn station in the village: Schmilka-Hirschmühle. There are regular express train connections from Germany and even from Austria to Bad Schandau (e.g. direct connection Berlin - Bad Schandau). From Bad Schandau, take the S-Bahn two stops to Schmilka, then take the old "Lena", the historic ferry from 1927, and you're there!