The B512 is a very short B-road in central London in an area of one-way streets.
It starts near St Pancras Hospital on the A5202. That road is on a one-way loop at this point but there is a short two-way section to allow B512 traffic to access the A5202 in both directions.
The B512 then heads west along Crowndale Road and reaches a set of traffic lights where it crosses the southbound A400. One block west the B512 becomes one-way westbound itself and it ends one block further west at a complicated traffic-light-controlled junction by Mornington Crescent tube station. The road to the left is the A4200; to the right is the northbound A400; straight across leads to an unclassified road running parallel to the northbound A400 but in the opposite direction providing local access.