Spot on terminal junkie. U1 uses the down loop after a manual point change.
It's actually Schierkeon the line to the Brocken.
It seems to be a timetabled move when a special from Wernigerode to the Brocken is run.
U1 is the special usually Mallet hauled, U2 is the next service train to the Brocken and folows the special. DW is a return service train.
To allow U2 to keep to its booked times it overtakes the special at Schierke.
Even more remarkable is that the line to the summit is a complete spiral. It's quite something to be on U2 and look up the mountain to see U1 coming round the spiral at a higher level 100 metres above your train. Although U2 is something like 5kms behind by rail.
The Harz system shows what can be done with a railway combining as it does steam hauled tourist trains all year round, enthusiasts specials including photo stops, a community rail service for the locals with railcars particualrly for school children, an extension of the Nordhausen tram system to serve the North Western suburbs and a heavy freight railway.
It can be done Portishead! Trams to Bristol centre, railcars to BTM▸ (Bristol Temple Meads (strictly, it should be BRI)) with a plume of steam for some services plus the freight. They can all run on the same rails.