route E70: Ljubljana–Zagreb–Sisak–Slavonski Brod–Belgrade European route E75: Belgrade–Niš–Skopje–Veles–Thessaloniki Legacy Since 1994 the route is also part of the Pan-European corridor X that extends from Salzburg to Thessaloniki. The road has been continuously upgraded. As of 2019, it is a modern motorway in its entire length through: Slovenia - the A2 motorway; Croatia - the A3 motorway; Serbia - the A3 motorway west of Belgrade and the A1 motorway south of Belgrade. North Macedonia - the A1 motorway. The most difficult section to engineer and build was the Grdelica Gorge section which was completed in May 2019. The classification as the M-1 Highway continued in Serbia up to 2013, when the road was reorganized as the A1 and A3. References Sources External links Socialist Federal Republic of Yugoslavia Controlled-access highways Roads in Croatia Roads in Slovenia Highways in Serbia Roads in North Macedonia