Travelling by train within Bulgaria remains the most popular form of transportation. However, road transportation has grown steadily in recent years. Bulgaria has many highway projects underway, including portions of the Trans-European Motorway, a route connecting Budapest with Athens via Vidin and Sofia and with Istanbul via eastern Bulgaria. There are 215 airports, 128 of which have paved runways. Sofia's Vrazhdebna Airport is the major air centre, but there are also international airports at Varna and Burgas, as well as seven major domestic airports.