An Autobahn vehicle is a type of car that is designed to be driven on the German Autobahn, which is a highway system with no speed limit. The three most common types of Autobahn vehicles are AUDI, Audis, and Opel, all of which have four or five letters in their name. AUDI is a German car manufacturer that produces luxury vehicles, Audis is the plural form of AUDI, and Opel is another German car manufacturer that produces cars, vans, and SUVs.