From Vienna or Munich:
Motorway Kufstein - Wörgl - Innsbruck - Landeck - Arlberg Expressway(S16) - Arlberg, Exit St. Anton/Arlberg (before the Arlberg Tunnel), then take the Federal road towards the Arlberg Pass - St. Christoph.

From Zürich:
Vaduz - Feldkirch - Bludenz - Exit Arlberg (before the Arlberg Tunnel) - towards Langen - Arlberg Pass - St. Christoph