When I remember correctly Gerrit mentioned that his homebrewn code is mostly written in VisualBasic. As far as I know, he studied business informatics.

However, they are also using other software like http://www.railware.com. I visited the Miniaturwunderland this year and it was quite fun to watch the operator team writing down RailWare bugs into their own excel sheets.

The Miniaturwunderland model railroad is definitely worth a visit for every programmer! Then you can imagine how difficult it is to change things in large complex systems without breaking something.