And then there's Boston, requiring doors on the left side of unidirectional vehicles (including trolleybuses) because of underground configurations which long predate the use of unidirectional vehicles. On the other hand, there is a streetcar line in Gmunden am Traunsee in Austria, connecting the town square with the OeBB station halfway up the hillside and meeting all trains; it's single track, without turning loops, all platforms are on the same side of the track, and it has (or had when I was there) bidirectional vehicles with doors on only one side.
It's a go: Streetcar finally opens notes that it opened on September 9.
Cincinnati's long-awaited streetcar opened its doors to the public at noon on Friday, and began running along the 3.6-mile loop through Downtown and Over-the-Rhine. It was the first time in 65 years Cincinnati had an operating streetcar.