The Brotherhood and Unity Highway (Serbo-Croatian: Autoput "Bratstvo i jedinstvo", "Братство и јединство"; Croatian: Autocesta "Bratstvo i jedinstvo"; Slovene: Avtocesta "Bratstvo in enotnost"; Macedonian: Автопат "Братство и единство") stretched over 1,180 km (730 mi) across former Yugoslavia, from the Austrian border at Rateče near Kranjska Gora in the northwest via Ljubljana, Zagreb, Belgrade and Skopje to Gevgelija on the Greek border in the southeast. It was coloquially named autoput or autocesta (generic Serbo-Croatian expressions for "highway", "motorway"), as it was the one and only modern highway in the country, connecting four constituent states. This use is gradually fading out after the successor states have built further motorways.
Construction began on initiative of President Josip Broz Tito, who called the project the "Road of brotherhood and unity" (Autoput bratstva i jedinstva) after the motto of the League of Communists of Yugoslavia. A first section between Zagreb and Belgrade built with the effort of the Yugoslav People's Army and volunteer Youth Labour Brigades opened in 1950.
In the 1960s and 70s the autoput became a much frequented holiday route for Turkish immigrants in West Germany and Austria (then called Gastarbeiter) visiting their original homeland during the summer vacation time, and for tourists to southeastern Europe. Entering communist but non-aligned Yugoslavia was far easier, for people from NATO countries such as Germany and Turkey, than entering any of the Warsaw Pact communist countries of the Balkan region that might have provided alternative routes.
Originally an ordinary road, the carriageway used to be congested with cars and trucks, especially in summertime, when overtired long-term drivers caused numerous accidents. Wrecked cars usually remained in place for long periods of time, providing a grim reminder of the dangers of this highway. The situation slightly improved after some parts were brought up to modern motorway standards (two lanes for each direction plus an emergency lane) on sections Kranj-Ljubljana (20 km), Zagreb-Slavonski Brod-Županja (259 km) and Sremska Mitrovica-Belgrade-Niš (277 km) from 1977 on.
In 1991 traffic almost completely discontinued due to the Yugoslav wars bringing severe damage to several sections.
Since 1975, the road was concurrent with the following routes of the International E-road network:
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 2011, it is a modern motorway in its entire length through Slovenia, the A2, as well as in Croatia as the A3 (including the Zagreb bypass). It is almost complete in Serbia as the Autoput 1 and the in Macedonia as the M-1 motorway.