This article is from the Bulgaria FAQ, by Dragomir R. Radev firstname.lastname@example.org with numerous contributions by others.
(by Jan Terziyski)
The airport is 3km from the Sofia living areas (Druzhba, Iskyr, etc.).
The buses depart every 20min, but in the rush hours you can get on
for 5 min or so. Tickets ARE AVAILABLE on board, but one has to by a
bunch of ten or five to ease the driver who may not have change. For the
tourists who have reserved rooms in bigger hotels by travelling agency,
there are buses going directly to the hotel(I know about Varna, but such
a service should be available in Sofia).
There are 4 main international roads, used by tourists and cargo-trucks:
Russe-Pleven-Sofia-Kulata and Russe-Sliven-(to Turkey and to Greece).