Hey, thanks a lot for your fast answer. I am also happy because are getting somewhere. I started a new game with only this mod enabled and the tech tree had no tech for bridges in it. I also examined all the descendants of "Advanced Electronics", but none enables bridges.
Then I examined the mod. I have the mod archive "cargo-ships_0.0.21.zip" installed in my mod folder. It as of today is outdated. I updated the mod and now the tech "Train bridges" is in it.
My conclusion is, I installed the mod when there were no bridges in it, did not use it, but just recently came back to read about the features of the mod. Sorry for the turmoil and thanks for your help!