Interesting video that, and illustrating the point I mentioned earlier. Note that some of the route shown in the video is not guided - only trolley, but the reserved track/road is used by all public transport - trams, Trolley buses, guides buses and diesel buses in that system.
The Essen trams run on metre gauge track meaning the buses can easily straddle the tracks, many non-integrated trams run metre gauge in Germany. The integrated (standard gauge) S-Bahn services have taken over old urban branches and travel quite long distances. Think Gateshead Metro or Croydon Tramlink and to some extent Manchester.
See the comment above about tram track gauge, but the loading gauge is obviously related. There seems to be a raft of problems with bus guidance gauges, both guide and loading. UK trams are wide a very long way down to the tracks not like older designs. This only presents a problem for the guides and the 'free' buses can travel on the inset track as in other UK systems.
The Essen and associated Ruhr/Rhine valley systems are really quite impressive in their integration, but they did end up with a lot of space to design it in post war years, rather than trying to fit systems into a very crowded townscape - no excuses for rural systems.