The O-3 runs from Edirne to Istanbul and is the only motorway in Turkey located entirely in Europe.

From there, the motorway passes through mostly rural farmland until it enters the Istanbul metropolis near Silivri.

[1] O-3 "Avrupa otoyolu" "Mahmutbey Batı K19" junction connects to O-7, E80, Istanbul Airport and Yavuz Sultan Selim Bridge in the north direction, to Ataturk Airport with the 2nd Beltway in the south direction.

The last junction of the European motorway "Mahmutbey Doğu K20" connects to O-2 motorway (2nd Beltway) and Fatih Sultan Mehmet Bridge in the east direction, to 1st Beltway (O-1) with the O3-O1 connection road in the south direction.

[2] The motorway has six lanes, three in each direction, except for a 44.6 km (27.7 mi) section between Silivri and Esenyurt.