The northern terminus of the A 9 is at the Potsdam interchange, where it merges into the A 10, also known as the "Berliner Ring", about 30 kilometres (19 mi) away from the Berlin city limits. The shortest route from there into Berlin would be the A 10 (east) and the A 115 (AVUS). The southern end is in the Munich borough of Schwabing.
On its way, the A 9 passes through the German states of Brandenburg, Saxony-Anhalt, Thuringia, and Bavaria. West of Leipzig, the border between Saxony-Anhalt and Saxony crisscrosses along the autobahn. In Bavaria, long sections of the Nuremberg–Munich high-speed railway run parallel to the autobahn.
Plans for a European motorway connection from Berlin to Rome were already developed from 1927 by a private MüLeiBerl (Munich-Leipzig-Berlin) company. However, construction of the A 9 was not begun until the 1930s as part of the project set up by . The bridge was later destroyed at the end of the war but rebuilt due to a West and East German cooperation until 1966. The river marked the inner German border
It was inaugurated in sections, beginning in 1936 with the Strecke 16 between what is today's Schkeuditz interchange (present-day A 9 and A 14) near Leipzig and Bad Berneck im Fichtelgebirge, 164 kilometres (102 mi) in length. With the opening of the second lane near Schnaittach in 1941, the last gap was closed. This makes the A 9 Germany's first completed autobahns.
After World War II, the section from the inner German border to Berlin served as one of four transit access roads through East Germany (GDR) toward West Berlin during the Cold War era. Yellow signs with "TRANSIT" in black letters marked the allowed route. Distances were usually given towards Berlin - Hauptstadt der DDR ("Berlin - Capital of the GDR"), i.e. East Berlin. Despite funding from West Germany, road conditions were generally poor. The surface was made up of 1930s concrete slabs rather than blacktop or continuously cast concrete. A section in Thuringia between Schleiz and the Rodaborn rest area even was a cobblestone road, later paved over by the East German authorities until being replaced by concrete in the 1980s. Until the introduction of a new numbering system in 1974, the southern part was known as the West German A 3.
After German reunification, the A 9 was to be extensively rebuilt and upgraded, being "German Unity Transport Project" No. 12. The old two-lane profile without emergency lane was in no way suited to modern levels of traffic, speed, and expected safety. In 1990, 50, 000 vehicles per day were counted near Bayreuth, about as much as the motorway could handle. After the work was finished near Bayreuth in 2006, the only part of the old profile was in Thuringia between the Schleiz and Triptis junctions. This construction was finished 2014, so there are at least three (and near Munich more) lanes plus emergency lane in each direction for the whole route. Only Hermsdorf interchange still has a short 2 lane section.
Current condition and future plans
With one exception, Hermsdorf interchange, the A 9 has a profile of at least three lanes and one emergency lane per direction. The section between Neufahrn and the München-Nord interchange north of Munich was upgraded between 2004 and 2006 to four lanes each way. A survey of this section conducted in 2008 recorded an average number of 143, 000 vehicles per day and a maximum of 184, 000.
Since 2006 talks have been underway about turning the three-way interchange Holledau into a four-way, and extending the A 93 into the Pfaffenhofen area. Further plans and visions include widening the Hermsdorfer Kreuz to six lanes, and widening the sections Nuremberg – Nuremberg-East and Holledau – Neufahrn to eight lanes.
On January 26, 2015 German transport minister Alexander Dobrindt announced plans to outfit an as yet undesignated section of the A9 in Bavaria as a test track for autonomous cars.
Along the routeVockerode Elbe Bridge tower, c. 1984
East of Dessau, the autobahn crosses the Elbe River via the 654 m (2, 146 ft) long Vockerode Bridge. Built in 1938 according to plans designed by Paul Bonatz, it was replaced by a new construction in the course of the A 9 extension from 1996 to 2000. The prominent tower at the northern end is preserved, it was widely known to transit travellers for its Plaste und Elaste aus Schkopau ("plastic and elastomer from Schkopau") neon sign, now on display at the German Historical Museum in Berlin.
Close to exit 10, Dessau-East, a gravel pit had provided material for the construction of the autobahn. After 1939 the pit was renaturated and became the "Reichsautobahnbad Mildensee", with cabins to change, and eateries. It is still in use today as a beach, but not under the old name.
The Dessauer Rennstrecke
South of exit 11, Dessau-South, nearly ten kilometers of the roadbed — roughly from Thurland southwards to just north of the B 183 interchange (exit 12 for Bitterfeld/Wolfen of the modern A9 roadbed) — were upgraded with a paved-over median to become the "Dessauer Rennstrecke" (Dessau Racetrack), a 25-meter (82 ft) wide high-speed track intended for races and record attempts, such as by Rudolf Caracciola in 1938/39 or those by Hans Stuck with the Mercedes-Benz T80 land speed record car, starting in January 1940. With its pillarless bridges, but especially with the straight alignment and the broad concrete surface without a distinct median, it was also intended to function as an auxiliary airfield in World War II. After the war, annual races were resumed from 1949 to 1956. The East German driver Paul Greifzu was killed in a training accident on 10 May 1952.
The four-way interchange at Schkeuditz was the first cloverleaf interchange in Germany, as well as the first autobahn interchange in Europe. It was opened in 1936, two years before construction was finished.