I see 2 trams in the Waltershausen loop, while Line 6 requires only 1 tram. What is the reason for that?

Last week, there was a closure to Tabarz for some hours on seperate days. Between the stations Friedrichroda and Tabarz, there were works on vegetation and the track. During these few hours, Line 4 was diverted to Waltershausen without reducing any tram (Line 4 has five trams, each round trip takes 2 hours and 30 minutes). Because no reducement on trams, they have round 40min break on this terminus and for some minutes two trams stay there.