From the North (in summer only):
Zell am See - Grossglockner road (reduction with the Glockner-Gold-Card)
Otherwise:
Munich - Kufstein - Mittersill - Felbertauern road - Lienz - Heiligenblut
From the East:
Vienna - Westautobahn motorway - Tauernautobahn motorway - Spittal/Drau - Heiligenblut