Construction. Similar to such freeways in other countries, autobahns have multiple lanes of traffic in each direction

Similar to such freeways in other countries, autobahns have multiple lanes of traffic in each direction, separated by a central barrier with grade-separated junctions and access restricted to certain types of motor vehicles only. The first German Autobahn was completed in 1932 between Cologne and Bonn (it was the world’s very first motorway!). Each carriageway was flanked by bankettes about 60 cm (2 ft) in width, constructed of varying materials; right-hand bankettes on many autobahns were later retrofitted to 120 cm (4 ft) in width when it was realized cars needed the additional space to pull off the autobahn safely. In the postwar years, a thicker asphaltic concrete cross-section with full paved hard shoulders came into general use. The top design speed was approximately 160 km/h (100 mph) in flat country but lower design speeds could be used in hilly or mountainous terrain. A flat-country autobahn constructed to published design standards in use during the Nazi period could support hands-off speeds on curves of about 150 km/h (95 mph).

The number signet for the “A 8” as it appears on all traffic signs

The current autobahn numbering system in use in Germany was introduced in 1974. All autobahns are named by using the capital letter “A” followed by a blank and a number (for example “A 8”). The “main autobahns” going all across Germany have a single digit number usually even-numbered for east-west routes and odd-numbered for north-south routes. Some roads may not be as easily distinguished as strictly either as it would be, for example, in the United States whose major roads follow routes that are clearly horizontal or vertical when viewed on a conventional map. Shorter autobahns that are of regional importance (e.g. connecting two major cities or regions within Germany) have a double digit number (e.g. A 24, connecting Berlin and Hamburg).

There are also very short autobahns of just local importance (e.g. beltways or the A 555 from Cologne to Bonn) that usually have three numbers the first one of which is similar to the system above, depending on the region.