The Rhine-Ruhr region covers the Ruhr area plus Düsseldorf, Wuppertal, Mönchengladbach, Krefeld etc. It's the biggest agglomeration of Germany.
Public transport consists of buses, trams, Stadtbahn, S-Bahn, monorail and regional trains.
I will begin with Stadtbahn.
Stadtbahn Rhein-Ruhr, Dortmund – car type B80C:
Type B80C8:
Stadtbahn Rhein-Ruhr, Bochum – car type B80D:
Stadtbahn Rhein-Ruhr, Essen – car type B80C former B100S:
Type P89:
Stadtbahn Rhein-Ruhr, Mülheim – car type B100S – photo taken in Essen Hbf.:
Stadtbahn Rhein-Ruhr, Duisburg – car type B80C – photo taken in Düsseldorf-Wittlaer:
Stadtbahn Rhein-Ruhr, Düsseldorf – car type B80D:
railfaneurope.net