in the Ruhr - district:
The tram - line on the photo has got double tracks, once
the standard gauge (1435 mm = 5 feet, like at the railroads)
for Duisburg´s tramway corporation, and once the narrow
gauce of one meter for Muelheim´s tramway corporation.
The reason: The tramways of the central Ruhr - district
are much elder, and the Prussian railroad administration
did only allowed narrow track tramways in fear of competition.