The A406 or the North Circular Road is a road which crosses North London, linking West and East London. The speed limit is either 30 or 50 mph depending on the stretch of the road, including the sections with multiple carriageways. It, together with the South Circular Road, 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. The Wikipedia article is [1]