German motorways (Autobahn) are numbered according to special rules.
(The "main autobahns" which go all the way across Germany have a single digit number usually even-numbered for east-west routes and odd-numbered for north-south routes. 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). Any very short autobahns, of local importance (such as beltways, or the A 555 from Cologne to Bonn) usually have three numbers.)