North Circular

The A406 or the North Circular Road is the 25.7 mile long road which crosses North London, UK, linking West and East London. The speed limit is 30, 40 or 50 mph depending on the stretch of the road, including the sections with multiple carriageways. Together with the South Circular Road, it forms a ring road through the inner part of Outer London. This ring road does not make a complete circuit of the city; being C-shaped rather than a complete loop as the crossing of the River Thames in the east is made on the Woolwich Ferry.

More information on the Wikipedia page