My first advice: Throw Cassellís German Dictionary out if those are the definitions it gives for Bahn. They do not capture the essence of a Bahn, namely that it is a very restricted or prescribed path. For eample, the orbit of a planet is called its Bahn in German, or a racetrack is called a Rennbahn, or the lanes of a competition swimming pool are called its Bahnen (plural of Bahn). A dictionary not giving orbit, track and lane for Bahn is simply no good. Anyway, the neologism Autobahn probably was formed based on this meaning--it is indeed a very prescribed and restricted route for a car.
So far, so good. But remember, I complained about the way Bahn was clued, namely in connection of what a Volkswagen could do. And there lies the problem, which has nothing to do with dictionary definitions, but with idiomatic usage. Every sentence I could think of, like "A Volkswagen fährt auf der Bahn" (a Volkswagen drives on the Bahn) or "A Volkswagen benützt die Bahn" (...uses the Bahn) ends up being nonsense b/c it means "A Volkwagen takes the train" or "...uses the train". As I said, in the context of transportation, Bahn means railroad, like in "Bahnhof" (railroad station).
Only a very good dictionary would enable you to understand this. But it would be of a size that would make it an impractical accessory on a date. Still, The "dictionary excuse" is unsatisfactory to me for the same reason that the "layman's understanding excuse" is unsatisfactory to a mathematician or physicist or whoever has complained about this in the past on the blog. What we are saying is this: There are always multiple ways to clue an answer (like Bahn does not have to be clued in connection with a Volkswagen). Is it too much to ask for clues that hold up under both a layperson's and an expert's scrutiny?