English subways have 'Cars', but English Surface Trains have 'Carriages'. Why the Difference?

I heard both terms used in an episode of 'Sherlock'. It seems like one term or the other should do for both surface and underground trains.

Solution 1:

I think this was explained in the episode of Sherlock. The terminology depends on who supplied the original carriages or coaches. In the case of the London Underground, it was the American company (American Car and Foundry), and the American term stuck with people employed in the London Underground. That is also why British trains have 'buffet cars'. Members of the public, however, are likely to use terminology from the railways and talk about carriages or coaches.

Solution 2:

I was on my way home on Saturday afternoon when an announcer of the recorded message on the Piccadilly line clearly asked passangers to 'move down inside the cars please'. Car as a term is clearly still in use on the tube....