The western A 4 starts north-west of Aachen, where the Dutch A76 enters Germany.

The eastern part starts at the Kirchheim intersection (with the A 7) and goes through Eisenach, Gotha, Erfurt, Weimar, Jena, Gera, Chemnitz, Dresden and Bautzen to Görlitz, where it crosses to Poland and continues as A4.

Eight kilometers down the road, after the Wommen interchange, the road crosses back into the former East Germany into Gerstungen (today in Thuringia) for seven kilometers before crossing back to the former West Germany at Wildeck.

Because of that, the section between Wommen and Wildeck-Obersuhl interchanges was closed and fell into decay during the Cold War.

[4] Reconstruction of the last section in Thuringia between Eisenach and Gotha near the former Inner German Border began in 2007 and required building 25 km (16 mi) of new road.

The A4 near Gummersbach, North Rhine-Westphalia was the site of the then-most expensive traffic accident in German history: On 26 August 2004, a BMW M3, whose driver had no driving license and was later found to be driving under the influence, collided with a truck carrying 33,000 litres of gasoline.

The truck crashed through a guardrail, fell off the Wiehltalbrücke and exploded, killing the driver.