London Underground area, published by National Rail and Transport for London, includes suburban railway services. The tube map came second in a BBC and London Transport Museum poll asking for a favourite UK design icon of the 20th century and the underground's 150th anniversary was celebrated by a Google Doodle on the search engine. While the first use of a roundel in a London transport context was the trademark of the London General Omnibus Company registered in 1905, it was first used on the Underground in 1908 when the UERL placed a solid red circle behind station nameboards on platforms to highlight
British Rail Class 501 jointly operated with London Underground's Bakerloo and District Lines. In 1970 the trains were converted to 3rd rail only operation, although the 4th rail was retained on sections of line which are shared with London Underground trains. The original electric scheme on these lines was at 630V DC, which was actually supplied at +420V in the outer electric rail and -210V in the centre one, a total potential difference of 630V. This was the same system as used at the time (and still employed today) by London Underground, and allowed Underground trains to run over the lines, from Queens Park