London is the starting point for a number of motorway routes. The M25 is an orbital motorway which enables vehicles to avoid travelling through central London and is one of the busiest motorways in Europe.
When it opened in 1906, the GNP&BR's line served 22 stations and ran for 14.17 kilometres (8.80 mi) between its western terminus at Hammersmith and its northern terminus at Finsbury Park. A short 720-metre (2,362 ft) branch connected Holborn to the Strand. Within the first year of opening it became apparent to the management and investors that the estimated passenger numbers for the GNP&BR and the other UERL lines were over-optimistic. Despite improved integration and cooperation with the other tube railways, the GNP&BR struggled financially. In 1933 it and the rest of the UERL were taken into public ownership. Today, the GNP&BR's tunnels and stations form the core central section of the London Underground's Piccadilly line.
Greathead developed and patented a number of improvements to the Barlow shield and the improved design carried their joint names. Greathead also developed the use of a segmented cast iron lining for the circular tunnel, erected in sections from which the shield was jacked forward. Greathead was then involved in the planning and construction of a number of railways in Britain and Ireland, until, in 1884, he was appointed engineer for the City and South London Railway, the world's first underground electric railway when it opened in 1890. Greathead subsequently worked on the Waterloo and City Railway, the Liverpool Overhead Railway and the early planning of the Central London Railway.