Roads, defined as a path connecting two points, are generally classified into a hierarchy. At the top of the hierarchy are freeways (US) (UK: motorways), which serve entirely a function of moving vehicles between other roads. Freeways are grade-separated and limited access, have high speeds and carry heavy flows. Below freeways are arterials. These may not be grade-separated, and while access is still generally limited, it is not limited to the same extent as freeways, particularly on older roads. These serve both a movement and an access function. Next are collector/distributor roads. These serve more of an access function, allowing vehicles to access the network from origins and destinations, as well as connecting with smaller, local roads, that have only an access function, and are not intended for the movement of vehicles with neither a local origin nor destination. Local roads are designed to be low speed and carry relatively little traffic.
The design of roads is specified in a number of design manual, including the AASHTO Policy on the Geometric Design of Streets and Highways (or Green Book). Relevant concerns include the alignment of the road, its horizontal and vertical curvature, its super-elevation or banking around curves, its thickness and pavement material, its cross-slope, and its width. Fundamentals of Transportation/Geography and Networks
In most countries, it usually refers to the German autobahn specifically. The recommended speed of the German autobahn is 130 km/h (81 mph), but there is no general speed limit. Austrian and Swiss autobahns have general speed limits of 130 km/h (81 mph) and 120 km/h (75 mph), respectively. In German, the word is pronounced as described above, and its plural is Autobahnen; in English, however, the segment "auto" is typically pronounced as in other English words such as "automobile". The official name of the autobahn in Germany is Bundesautobahn (BAB) (Federal Freeway). Autobahns are built and maintained by the federal government (as are the federal highways), thus the name "Federal Freeway". The first were built in the 1920s, and in the 1930s the official name was "Reichsautobahn" (Freeways of the Reich).
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