The A5109 is a semi-urban A-road in north London. Originally the B553, it gained its current number in the 1940s.
The road starts at traffic lights on the A5 at Edgware General Hospital (opposite is the unclassified Camrose Avenue). It heads east along Deansbrook Road, going over the Edgware branch of the Northern Line, then turns left at a roundabout into Deans Lane. The A5100 Hale Lane is crossed between adjacent mini-roundabouts and the A5109 becomes Selvage Lane and forms the border of the London postal district: one side is HA8 (Edgware) and the other is NW7 (Mill Hill).
After going over the Midland Main Line and M1 it becomes the "annoying stranger" at Apex Corner where the A1 and A41 merge / split (depending which way you are heading). It sneaks along the A1 Barnet Way for a few yards before heading right at traffic lights into Marsh Lane, which merges with the B552 at Highwood Hill and takes its name, before becoming Totteridge Common; this section is surprisingly rural for the area. After passing through Totteridge, which has the air of a Home Counties village, we continue onto Totteridge Lane and become urban once more. We climb over the Barnet branch of the Northern line, passing Totteridge & Whetstone station. On reaching the A1000 soon afterwards the number changes on the far side of the staggered crossroads dropping the 5 and becoming just the A109 for Oakleigh Road North.