Amsterdam tram line 8 can never be used again… the reason is fascinating!
The Amsterdam tramway network has been around since 1875 and is currently one of the largest in the world. As of 2013, there are 15 lines running 216 trams, with 80.5km (50 miles) of track.
For much of WWII, the Netherlands were in the hands of the Nazis. As a result of this, one of the tram lines in Amsterdam's tramway network was used to deport Jews and, therefore, the number has never been used again. This was line 8 and was in use from 1905 to 1942. Other lines were also discontinued after the war, including lines 6, 14, 22 and 23, although 14 is now in use as a bus route.
There have been a lot of tram lines discontinued over the years. There are 12 line numbers that have been in use in the past that are no longer used, and a total of 27 have been used. Those all numbered 1-27, while 30 is used informally by the Electric Tramway Museum Amsterdam. Numbers 28 and 29 have never been used.