Indeed, the fairly recently opened trolley bus route 90 in Rome is like that. We just came back from 6 weeks in Europe and I must confess, knew nothing of this line until I saw a trolley (with poles down) pass me in the street so, I went for a ride. The wire starts just outside the city edge and about a block later crosses it's only interesting infrastructure where it crosses tram line 3. One has to wonder why they didn't start it after the tram crossing! Anyway, it's a long route and the wire forms a long U shape as it has no other junction or switch. The route is interesting and it's tramway history can be seen on the wider streets where (as in other places in Rome) the centre is "reserved" (observed by-not many!!) for buses with little domes beside a very wide "track" and has conventional tram safety zones at the stops (so why did they take the trams away???). At the terminus, the wire just continues around without any layover prevision yet there are several bays.

Most of the buses are Solaris which are fast and quiet and, when off wire, they are battery powered. The overhead has several location where there are covered areas of over head so the poles can be electrically raised and I saw this on several occasions, once at the term when a bus following, dropped his poles and took off to raise them in a later section. The latest buses are Ansaldo's and they are diesels off wire.

An interesting operation but oddly, the area off wire (from city edge to Termini) is some of the most unattractive of the whole line, indeed termini, like most of Rome outside the absolute tourist areas is rather filthy and disappointing for such a supposed world class city but that's another story.