The ring road is also the boundary of the London Congestion Charge zone. Starting at the northernmost point and moving clockwise, the roads defining the boundary are Pentonville Road, City Road, Old Street, Commercial Street, Mansell Street, Tower Bridge Road, New Kent Road, Elephant and Castle, Vauxhall Bridge Road, Park Lane, Edgware Road, Marylebone Road and Euston Road.
The roads are described as the inner ring road because there are two further sets of roads that have been described as London ring roads. The north and south circular roads together form the second ring road around London, roughly 10 miles in diameter. The M25 motorway is the outermost road encircling the city, at an average diameter of 40-50 miles.
See also: List of London roads.