Historical version 3 of Metropolitan Line (view current version)
The Metropolitan Line is peculiar in that its rolling stock has very tall and wide carriages. It shares these with the East London Line. To understand the reasons for this, it is necessary to understand the history of the Metropolitan Railway Company.
Prior to the nationalisation of British Railways, one of the more ambitious companies was the Metropolitan Railway Company. They ran trains from Aldgate Station, out as far as Aylesbury and beyond. They had ambitions to extend this line out to Birmingham and Manchester, but this did not happen, as other companies were given licences to run services from Euston station. The Central London sections of the Metropolitan's track became part of the tube network, but the others were absorbed into the Chiltern line.
One of the factors and selling points with the Metropolitan's trains was comfort. The Metropolitan specified larger dimensions of tunnels than the other operating companies, and had their own stock which was wider, although this is much closer to the spec of overground trains, and similar in bodywork to the 313 units operated by Silverlink.
Another reason for different rolling stock is the higher top speed which the trains are comfortably capable of. The Metropolitan Line operates what could be described as an express service to places such as Amersham, Uxbridge and Watford. This includes fast trains, which are non-stopping at Wembley Park, [Preston Road]? and [Northwick Park]?.
Both the East London Line, and the GN Electrics Line were originally run by the Metropolitan Railway Conpany, hence have tunnelling capable of carrying the wider, taller trains. The East London Line carries the same rolling stock as the Metropolitan Line, but the GN Electrics Line is run by WAGN, and carries 313 units.