Here is a picture of a route 51 Metro train at Overamstel station in the southern district of Amsterdam.
It didn't quite happen like that. There were vehement protests at the possible loss of traditional tramways and, of course, the inevitable financial reviews. The present network has part of the 1968 plan still recognisable.
The yellow (54) line goes no further than Centraal Station.
The red (53) joins it.
A third route orange (51) uses the same tracks, turning right to Amsterdam Zuid station and then south the Amstelveen.
The circular route green (50) only circles part way before joining the 54 to the south east.
A remnant of the blue (52) north south service will be opened in 2017.
Which brings is back to our mysterious friend, Metro 51 in a fruity orange colour on the maps but with a colour coded route box in the destination screens ...
... just like a tram.
And that's the answer. For political reasons, all about not getting rid of trams, the 51 Metro (with third rail pick up) gets to Amsterdam Zuid station ...
... where it changes to pantograph pick-up, drops down to road level and, effectively becomes tram 51 running with tram 5 for a while. The stations have double-height platforms; low for tram 5 and high for tram/metro 51. This little video clip shows a new-ish tram on line 5 passing the high platform and stopping at the tram level bit.
Line 51 is sometimes referred to as the Sneltram, the fast tram.
Usually the tram and Metro system functions like clockwork; but occasionally there is the odd prang. Here a Metro 51 collided with a tram 5.
But it is the headline that fbb liked. The chubby one struggles with understanding written Dutch and finds the spoken tongue impossible. But you would never mistake this headline.
Not a good idea for one tram to botst op another. But none of the vier was seriously gewonden.