The kilometre reading was one dead giveaway, if someone knows to check the Wiki page. But you could have had it easier. The river is clearly a major river (major for Germany) -- and the entire line from Hannover to Würzburg crosses only two, the Main (twice) and the final, wider part of the Fulda (again twice). (The other line of similar age, Mannheim-Stuttgart, crosses none.) Of the four bridges, only the Maintalbrücke Gemünden fits the geography.

_{*Lunatic*, n.
One whose delusions are out of fashion.}