A 2017 report by the Federal Road Research Institute reported that in 2015 70.4% of the autobahn network had only the advisory speed limit, 6.2% had temporary speed limits due to weather or traffic conditions, and 23.4% had permanent speed limits.[2] Measurements from the German state of Brandenburg in 2006 showed average speeds of 142 km/h (88 mph) on a 6-lane section of autobahn in free-flowing conditions.[3]
Source: https://en.wikipedia.org/wiki/Autobahn
If Germany wants to get serious about saving fuel, speed limits on every section of the autobahn network are absolutely necessary. Dropping speed from an average of 142 km/h to 100 km/h would result in very significant savings in fuel consumption. At motorway speeds, air resistance is dominant. Air resistance is proportional to the square of speed, which means that, roughly speaking, driving 142 km/h consumers twice as much fuel than driving 100 km/h. The rolling resistance of tires and the internal resistance of the engine are also higher at higher speeds but that increase is dwarfed by the difference in air resistance.
Due to the sanctions and counter sanctions the cost of energy will go up considerably in the coming winter. Reducing high speeds on German motorways is a no-brainer for Germans to save money to afford the drastically higher price of natural gas to be expected come winter as a large share of homes in Germany are heated with gas.
The lack of speed limits on most sections of German motorways is unique in the world. In Austria, the highest speed limit is 130 km/h. In Finland, it's 120 km/h and in Sweden it is 110 km/h. With all the talk about the energy shift and going green, it is quite unbelievable that there still exist sections of motorways without speed limits.
Fortunately, German winters tend to be mild and relatively short. One way to save gas in heating is through the use of air source heat pumps. They require power but produce three times as much heat as direct electrical heating.