Bundesautobahn 4 (translates from German as Federal Motorway 4, short form Autobahn 4, abbreviated as BAB 4 or A 4) is an autobahn that crosses Germany in a west-east direction. The western segment has a length of 156 km (97 mi), the part in the east is 429 km (267 mi) long. Works to continue the A 4 are in progress, but currently no plans exist to fill the gap completely.
The A 4 starts north-west of Aachen, where the Dutch A76 enters Germany. Initially it is 2 lanes each way with no speed limit. From Kreuz Aachen to Düren and from Kerpen to Refrath (between Refrath and Köln-Merheim westbound the hard shoulder is the 3rd lane and only open at peak times) it has 3 lanes each way. Between Kreuz Köln-West and Kreuz Heumar it forms the southern part of the Cologne Beltway (Kölner Autobahnring). Between Eschweiler and Kreuz Aachen westbound there is a speed limit of 120 km/h. The whole rest of the section between Kreuz Aachen and Kreuz Köln-West has a variable speed limit. Between Kreuz Köln-West and Kreuz Heumar the speed limit is 120 km/h. From Kreuz Köln-Ost to Refrath there is a maximum limit of 100 km/h. The westbound section between Köln-Merheim and Kreuz Köln-Ost is restricted to 80 km/h. The section between Refrath and the current terminus at Krombach has no speed limit. Only between Untereschbach and Refrath westbound there is a 100 km/h speed limit from 6 - 10 am on weekdays. It is mostly 2 lanes each way, but between Untereschbach and Wiehl there are several additional climbing lanes in both directions.
The eastern part starts at the Kirchheim intersection (with the A 7) and goes through Eisenach, Gotha, Erfurt, Weimar, Jena, Gera, Chemnitz and Dresden to Görlitz, where it crosses the border to Poland and continues as A4 (PL).
The westernmost 11 kilometers of the A 4 form the most easterly stretch of the European route E314: continuing east from the Aachen interchange (Kreuz Aachen), the A 4 is part of the European route E40. European routes don't have gaps and E40 follows A 45 and A 5, which is a suitable route past the gap of A 4.
The first sections of the A 4 were built in the years 1934 to 1937. Because it crossed the border between East and West Germany several times, those parts were closed and fell into decay during the time of German division. Repairs of those parts are scheduled to be completed in 2007.
The "Wiehltalbrücke" is a bridge which carries the A 4 across the valley of the river Wiehl. The A 4 near Gummersbach, North Rhine-Westphalia was the site of the most expensive traffic accident in German history: On 26 August 2004, a BMW M3, whose driver did not hold a driving licence and was later found to be driving under the influence, collided with a tanker lorry, carrying 33,000 litres of gasoline. The lorry broke through a guardrail, fell off the Wiehltalbrücke and exploded, killing the driver. The subsequent fire caused severe structural damage to the bridge. The driver of the sports car involved in the accident was jailed for 22 months without parole in September 2005.
The bridge was closed for weeks until temporary repairs were completed. Permanent repairs began on July 28, 2006, and finished August 22, 2006, using a unique method never before used in Germany. For the duration of the repairs, where among other things a 20 m × 31 m segment was replaced, the bridge was closed. The repairs cost € 7.2 million.