For those who are looking for German railways operation and signalling principles especially in English, I highly recommended the following:

Source: Mark Vogel (Flickr.com)

Dr. Joern Pachl wrote an excellent document on the German railway operation principles (PDF), explaining in detail how the German system works compared to Anglo-Saxon’s.

Wolfgang Meyenberg did an excellent job on documenting and explaining the various German railways signal principles from last 2 centuries as well as the latest practices.

I hope both references will be useful to you in building a close to prototype railway operations on your model layout.