The (; German plural ) is the federal controlled-access highway system in Germany. The official German term is (abbreviated BAB), which translates as 'federal motorway'. The literal meaning of the word is 'Federal Auto(mobile) Track'. German have no federally mandated general speed limit for some classes of vehicles. However, limits are posted and enforced in areas that are urbanised, substandard, accident-prone, or under construction. On speed-unrestricted stretches, an advisory speed limit () of applies. While driving faster is not illegal in the absence of a speed limit, it can cause an increased liability in the case of a collision (which mandatory auto insurance has to cover); courts have ruled that an "ideal driver" who is exempt from absolute liability for "inevitable" tort under the law would not exceed . 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. Measurements from the German state of Brandenburg in 2006 showed average speeds of on a 6-lane section of Autobahn in free-flowing conditions. Network map Names Only federally built controlled-access highways with certain construction standards including at least two lanes per direction are called Bundesautobahn. They have their own white-on-blue signs and numbering system. In the 1930s, when construction began on the system, the official name was Reichsautobahn. Various other controlled-access highways exist on the federal (Bundesstraße), state (Landesstraße), district, and municipal level but are not part of the Autobahn network and are officially referred to as Kraftfahrstraße (with rare exceptions, like A 995 Munich-Giesing–Brunntal until 2018). These highways are considered autobahnähnlich (autobahn-like) and are sometimes colloquially called Gelbe Autobahn (yellow autobahn) because most of them are Bundesstraßen (federal highways) with yellow signs. Some controlled-access highways are classified as "Bundesautobahn" in spite of not meeting the autobahn construction standard (for example, the A 62 near Pirmasens). Similar to some other German words, the term autobahn when used in English is usually understood to refer specifically to the national highway system of Germany, whereas in German the word autobahn is applied to any controlled highway in any country. For this reason in German, the more specific term Bundesautobahn is strongly preferred when the intent is to make specific reference to Germany's Autobahn network. Construction Similar to high-speed motorways in other countries, autobahns