Speed limits in Germany
In 1973, in the wake of the 1973 oil crisis, a federal speed limit of 100 km/h (62 mph) on Autobahns was imposed to help conserve fuel for fear of impending future shortages (not for environmental or safety reasons). The measure only lasted from December 1973 to March 1974; while the administration and the Bundestag were in favor of keeping the speed limit, the Bundesrat pushed to repeal the law. As a compromise, a "recommended speed" was introduced on Autobahns and "highways outside of built-up areas with a center divide or without a center divide and a continuous lane for overtaking in both directions". This law is basically still in effect today. Unrestricted non-Autobahn highways, however, have since become virtually non-existent or replaced by "Schnellstraßen", Autobahn-like expressways typically limited to 120 or 130 km/h and normally only covering a few kilometers.
Bundesautobahn 4
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). The whole rest of the section between Kreuz Aachen and Kreuz Köln-West has a variable speed limit. Between Merzenich and Elsdorf, there is a speed limit of 130 km/h, that has been imposed in 2017, due to an increase of accidents. 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.